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 $226.44   4.501%   $236.6321   $236.63   $236.65   $236.60  
  Purchase #2 $194.37   3.706%   $201.5734   $201.57   $201.55   $201.60  
  Purchase #3 $16.85   4.469%   $17.603   $17.60   $17.60   $17.60  
  Purchase #4 $64.29   7.408%   $69.0526   $69.05   $69.05   $69.10  
  Purchase #5 $33.38   6.450%   $35.533   $35.53   $35.55   $35.50  
  Purchase #6 $52.41   4.835%   $54.944   $54.94   $54.95   $54.90  
  Purchase #7 $193.45   3.388%   $200.0041   $200.00   $200.00   $200.00  
  7 purchase totals = $781.19       $815.3422   $815.32   $815.35   $815.30