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 $57.53   8.248%   $62.2751   $62.28   $62.30   $62.30  
  Purchase #2 $226.89   13.563%   $257.6631   $257.66   $257.65   $257.70  
  Purchase #3 $33.68   8.429%   $36.5189   $36.52   $36.50   $36.50  
  Purchase #4 $6.64   4.379%   $6.9308   $6.93   $6.95   $6.90  
  Purchase #5 $78.85   13.299%   $89.3363   $89.34   $89.35   $89.30  
  Purchase #6 $57.70   10.268%   $63.6246   $63.62   $63.60   $63.60  
  Purchase #7 $235.88   11.597%   $263.235   $263.24   $263.25   $263.20  
  7 purchase totals = $697.17       $779.5838   $779.59   $779.60   $779.50