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 $147.86   9.470%   $161.8623   $161.86   $161.85   $161.90  
  Purchase #2 $221.51   7.158%   $237.3657   $237.37   $237.35   $237.40  
  Purchase #3 $250.69   8.581%   $272.2017   $272.20   $272.20   $272.20  
  Purchase #4 $53.82   12.832%   $60.7262   $60.73   $60.75   $60.70  
  Purchase #5 $114.63   5.280%   $120.6825   $120.68   $120.70   $120.70  
  Purchase #6 $88.79   9.252%   $97.0049   $97.00   $97.00   $97.00  
  Purchase #7 $22.86   5.733%   $24.1706   $24.17   $24.15   $24.20  
  7 purchase totals = $900.16       $974.0139   $974.01   $974.00   $974.10