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 $217.26   12.866%   $245.2127   $245.21   $245.20   $245.20  
  Purchase #2 $41.97   8.187%   $45.4061   $45.41   $45.40   $45.40  
  Purchase #3 $60.47   3.579%   $62.6342   $62.63   $62.65   $62.60  
  Purchase #4 $191.87   13.232%   $217.2582   $217.26   $217.25   $217.30  
  Purchase #5 $179.98   3.573%   $186.4107   $186.41   $186.40   $186.40  
  Purchase #6 $224.52   10.274%   $247.5872   $247.59   $247.60   $247.60  
  Purchase #7 $149.67   4.453%   $156.3348   $156.33   $156.35   $156.30  
  7 purchase totals = $1,065.74       $1,160.8439   $1,160.84   $1,160.85   $1,160.80