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 $63.53   8.561%   $68.9688   $68.97   $68.95   $69.00  
  Purchase #2 $154.39   11.122%   $171.5613   $171.56   $171.55   $171.60  
  Purchase #3 $136.54   9.718%   $149.809   $149.81   $149.80   $149.80  
  Purchase #4 $100.46   5.693%   $106.1792   $106.18   $106.20   $106.20  
  Purchase #5 $112.68   3.277%   $116.3725   $116.37   $116.35   $116.40  
  Purchase #6 $31.60   12.805%   $35.6464   $35.65   $35.65   $35.60  
  Purchase #7 $211.73   5.522%   $223.4217   $223.42   $223.40   $223.40  
  7 purchase totals = $810.93       $871.9589   $871.96   $871.90   $872.00