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 $84.37   12.224%   $94.6834   $94.68   $94.70   $94.70  
  Purchase #2 $11.31   7.693%   $12.1801   $12.18   $12.20   $12.20  
  Purchase #3 $25.52   9.484%   $27.9403   $27.94   $27.95   $27.90  
  Purchase #4 $230.32   6.567%   $245.4451   $245.45   $245.45   $245.40  
  Purchase #5 $95.66   4.412%   $99.8805   $99.88   $99.90   $99.90  
  Purchase #6 $42.92   3.414%   $44.3853   $44.39   $44.40   $44.40  
  Purchase #7 $218.41   8.589%   $237.1692   $237.17   $237.15   $237.20  
  7 purchase totals = $708.51       $761.6839   $761.69   $761.75   $761.70