Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $184.73   11.694%   $206.3323   $206.33   $206.35   $206.30  
  Purchase #2 $248.95   7.515%   $267.6586   $267.66   $267.65   $267.70  
  Purchase #3 $111.81   10.643%   $123.7099   $123.71   $123.70   $123.70  
  Purchase #4 $113.88   4.679%   $119.2084   $119.21   $119.20   $119.20  
  Purchase #5 $233.50   3.633%   $241.9831   $241.98   $242.00   $242.00  
  Purchase #6 $156.47   11.470%   $174.4171   $174.42   $174.40   $174.40  
  Purchase #7 $173.83   11.859%   $194.4445   $194.44   $194.45   $194.40  
  7 purchase totals = $1,223.17       $1,327.7539   $1,327.75   $1,327.75   $1,327.70