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 $65.55   4.823%   $68.7115   $68.71   $68.70   $68.70  
  Purchase #2 $201.55   5.629%   $212.8952   $212.90   $212.90   $212.90  
  Purchase #3 $118.78   5.395%   $125.1882   $125.19   $125.20   $125.20  
  Purchase #4 $82.59   4.679%   $86.4544   $86.45   $86.45   $86.50  
  Purchase #5 $82.91   6.174%   $88.0289   $88.03   $88.05   $88.00  
  Purchase #6 $123.52   13.139%   $139.7493   $139.75   $139.75   $139.70  
  Purchase #7 $227.88   11.763%   $254.6855   $254.69   $254.70   $254.70  
  7 purchase totals = $902.78       $975.7130   $975.72   $975.75   $975.70