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 $213.90   12.754%   $241.1808   $241.18   $241.20   $241.20  
  Purchase #2 $222.62   6.243%   $236.5182   $236.52   $236.50   $236.50  
  Purchase #3 $88.84   10.547%   $98.21   $98.21   $98.20   $98.20  
  Purchase #4 $244.57   10.275%   $269.6996   $269.70   $269.70   $269.70  
  Purchase #5 $82.57   6.152%   $87.6497   $87.65   $87.65   $87.60  
  Purchase #6 $87.29   4.311%   $91.0531   $91.05   $91.05   $91.10  
  Purchase #7 $185.28   5.858%   $196.1337   $196.13   $196.15   $196.10  
  7 purchase totals = $1,125.07       $1,220.4451   $1,220.44   $1,220.45   $1,220.40