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 $75.26   12.445%   $84.6261   $84.63   $84.65   $84.60  
  Purchase #2 $226.35   4.834%   $237.2918   $237.29   $237.30   $237.30  
  Purchase #3 $180.62   13.683%   $205.3342   $205.33   $205.35   $205.30  
  Purchase #4 $197.40   3.843%   $204.9861   $204.99   $205.00   $205.00  
  Purchase #5 $109.64   12.141%   $122.9514   $122.95   $122.95   $123.00  
  Purchase #6 $98.64   12.479%   $110.9493   $110.95   $110.95   $110.90  
  Purchase #7 $90.91   7.204%   $97.4592   $97.46   $97.45   $97.50  
  7 purchase totals = $978.82       $1,063.5981   $1,063.60   $1,063.65   $1,063.60