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 $219.65   13.595%   $249.5114   $249.51   $249.50   $249.50  
  Purchase #2 $234.71   12.778%   $264.7012   $264.70   $264.70   $264.70  
  Purchase #3 $235.45   3.838%   $244.4866   $244.49   $244.50   $244.50  
  Purchase #4 $36.42   7.384%   $39.1093   $39.11   $39.10   $39.10  
  Purchase #5 $209.34   8.183%   $226.4703   $226.47   $226.45   $226.50  
  Purchase #6 $132.94   13.534%   $150.9321   $150.93   $150.95   $150.90  
  Purchase #7 $50.91   8.481%   $55.2277   $55.23   $55.25   $55.20  
  7 purchase totals = $1,119.42       $1,230.4386   $1,230.44   $1,230.45   $1,230.40