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 $35.68   3.764%   $37.023   $37.02   $37.00   $37.00  
  Purchase #2 $60.66   8.194%   $65.6305   $65.63   $65.65   $65.60  
  Purchase #3 $82.74   11.465%   $92.2261   $92.23   $92.25   $92.20  
  Purchase #4 $26.76   7.548%   $28.7798   $28.78   $28.80   $28.80  
  Purchase #5 $31.63   5.653%   $33.418   $33.42   $33.40   $33.40  
  Purchase #6 $54.83   8.642%   $59.5684   $59.57   $59.55   $59.60  
  Purchase #7 $210.28   13.758%   $239.2103   $239.21   $239.20   $239.20  
  7 purchase totals = $502.58       $555.8561   $555.86   $555.85   $555.80