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 $69.62   8.849%   $75.7807   $75.78   $75.80   $75.80  
  Purchase #2 $220.58   10.416%   $243.5556   $243.56   $243.55   $243.60  
  Purchase #3 $231.54   5.427%   $244.1057   $244.11   $244.10   $244.10  
  Purchase #4 $35.56   3.822%   $36.9191   $36.92   $36.90   $36.90  
  Purchase #5 $245.29   4.668%   $256.7401   $256.74   $256.75   $256.70  
  Purchase #6 $85.97   13.779%   $97.8158   $97.82   $97.80   $97.80  
  Purchase #7 $231.29   10.666%   $255.9594   $255.96   $255.95   $256.00  
  7 purchase totals = $1,119.85       $1,210.8764   $1,210.89   $1,210.85   $1,210.90