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 $204.74   9.507%   $224.2046   $224.20   $224.20   $224.20  
  Purchase #2 $201.33   5.449%   $212.3005   $212.30   $212.30   $212.30  
  Purchase #3 $12.74   5.340%   $13.4203   $13.42   $13.40   $13.40  
  Purchase #4 $42.29   7.511%   $45.4664   $45.47   $45.45   $45.50  
  Purchase #5 $78.30   3.686%   $81.1861   $81.19   $81.20   $81.20  
  Purchase #6 $113.52   7.695%   $122.2554   $122.26   $122.25   $122.30  
  Purchase #7 $232.28   12.229%   $260.6855   $260.69   $260.70   $260.70  
  7 purchase totals = $885.20       $959.5188   $959.53   $959.50   $959.60