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 $201.48   5.245%   $212.0476   $212.05   $212.05   $212.00  
  Purchase #2 $101.90   13.668%   $115.8277   $115.83   $115.85   $115.80  
  Purchase #3 $70.50   5.224%   $74.1829   $74.18   $74.20   $74.20  
  Purchase #4 $119.31   6.229%   $126.7418   $126.74   $126.75   $126.70  
  Purchase #5 $138.54   11.240%   $154.1119   $154.11   $154.10   $154.10  
  Purchase #6 $246.97   12.318%   $277.3918   $277.39   $277.40   $277.40  
  Purchase #7 $16.49   5.742%   $17.4369   $17.44   $17.45   $17.40  
  7 purchase totals = $895.19       $977.7406   $977.74   $977.80   $977.60