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 $104.89   13.723%   $119.2841   $119.28   $119.30   $119.30  
  Purchase #2 $238.47   10.123%   $262.6103   $262.61   $262.60   $262.60  
  Purchase #3 $232.91   12.806%   $262.7365   $262.74   $262.75   $262.70  
  Purchase #4 $73.52   9.336%   $80.3838   $80.38   $80.40   $80.40  
  Purchase #5 $15.26   6.201%   $16.2063   $16.21   $16.20   $16.20  
  Purchase #6 $219.46   12.685%   $247.2985   $247.30   $247.30   $247.30  
  Purchase #7 $179.86   12.289%   $201.963   $201.96   $201.95   $202.00  
  7 purchase totals = $1,064.37       $1,190.4825   $1,190.48   $1,190.50   $1,190.50