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 $64.52   5.547%   $68.0989   $68.10   $68.10   $68.10  
  Purchase #2 $182.69   12.225%   $205.0239   $205.02   $205.00   $205.00  
  Purchase #3 $30.47   5.179%   $32.048   $32.05   $32.05   $32.00  
  Purchase #4 $83.76   11.293%   $93.219   $93.22   $93.20   $93.20  
  Purchase #5 $113.34   7.569%   $121.9187   $121.92   $121.90   $121.90  
  Purchase #6 $217.25   9.664%   $238.245   $238.25   $238.25   $238.20  
  Purchase #7 $95.43   7.819%   $102.8917   $102.89   $102.90   $102.90  
  7 purchase totals = $787.46       $861.4452   $861.45   $861.40   $861.30