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 $111.55   5.146%   $117.2904   $117.29   $117.30   $117.30  
  Purchase #2 $232.84   4.203%   $242.6263   $242.63   $242.65   $242.60  
  Purchase #3 $18.45   11.693%   $20.6074   $20.61   $20.60   $20.60  
  Purchase #4 $68.74   5.144%   $72.276   $72.28   $72.30   $72.30  
  Purchase #5 $128.26   10.368%   $141.558   $141.56   $141.55   $141.60  
  Purchase #6 $97.80   13.441%   $110.9453   $110.95   $110.95   $110.90  
  Purchase #7 $165.42   5.749%   $174.93   $174.93   $174.95   $174.90  
  7 purchase totals = $823.06       $880.2334   $880.25   $880.30   $880.20