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 $143.97   11.629%   $160.7123   $160.71   $160.70   $160.70  
  Purchase #2 $45.25   13.161%   $51.2054   $51.21   $51.20   $51.20  
  Purchase #3 $24.96   10.210%   $27.5084   $27.51   $27.50   $27.50  
  Purchase #4 $61.85   11.472%   $68.9454   $68.95   $68.95   $68.90  
  Purchase #5 $205.78   5.745%   $217.6021   $217.60   $217.60   $217.60  
  Purchase #6 $201.26   8.241%   $217.8458   $217.85   $217.85   $217.80  
  Purchase #7 $122.26   8.133%   $132.2034   $132.20   $132.20   $132.20  
  7 purchase totals = $805.33       $876.0228   $876.03   $876.00   $875.90