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 $58.41   8.146%   $63.1681   $63.17   $63.15   $63.20  
  Purchase #2 $42.79   13.732%   $48.6659   $48.67   $48.65   $48.70  
  Purchase #3 $217.52   6.148%   $230.8931   $230.89   $230.90   $230.90  
  Purchase #4 $62.91   10.419%   $69.4646   $69.46   $69.45   $69.50  
  Purchase #5 $179.27   9.854%   $196.9353   $196.94   $196.95   $196.90  
  Purchase #6 $250.80   12.583%   $282.3582   $282.36   $282.35   $282.40  
  Purchase #7 $42.29   5.253%   $44.5115   $44.51   $44.50   $44.50  
  7 purchase totals = $853.99       $935.9967   $936.00   $935.95   $936.10