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 $65.88   5.608%   $69.5746   $69.57   $69.55   $69.60  
  Purchase #2 $194.42   7.856%   $209.6936   $209.69   $209.70   $209.70  
  Purchase #3 $134.89   12.114%   $151.2306   $151.23   $151.25   $151.20  
  Purchase #4 $54.72   11.295%   $60.9006   $60.90   $60.90   $60.90  
  Purchase #5 $245.26   6.181%   $260.4195   $260.42   $260.40   $260.40  
  Purchase #6 $108.46   8.657%   $117.8494   $117.85   $117.85   $117.80  
  Purchase #7 $37.39   6.709%   $39.8985   $39.90   $39.90   $39.90  
  7 purchase totals = $841.02       $909.5668   $909.56   $909.55   $909.50