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 $162.92   8.675%   $177.0533   $177.05   $177.05   $177.10  
  Purchase #2 $58.51   8.201%   $63.3084   $63.31   $63.30   $63.30  
  Purchase #3 $61.46   5.557%   $64.8753   $64.88   $64.90   $64.90  
  Purchase #4 $43.52   6.183%   $46.2108   $46.21   $46.20   $46.20  
  Purchase #5 $77.71   9.819%   $85.3403   $85.34   $85.35   $85.30  
  Purchase #6 $80.45   9.865%   $88.3864   $88.39   $88.40   $88.40  
  Purchase #7 $167.36   13.822%   $190.4925   $190.49   $190.50   $190.50  
  7 purchase totals = $651.93       $715.6670   $715.67   $715.70   $715.70