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 $84.67   11.634%   $94.5205   $94.52   $94.50   $94.50  
  Purchase #2 $26.79   4.426%   $27.9757   $27.98   $28.00   $28.00  
  Purchase #3 $129.96   11.551%   $144.9717   $144.97   $144.95   $145.00  
  Purchase #4 $13.91   10.662%   $15.3931   $15.39   $15.40   $15.40  
  Purchase #5 $244.78   8.490%   $265.5618   $265.56   $265.55   $265.60  
  Purchase #6 $172.90   12.504%   $194.5194   $194.52   $194.50   $194.50  
  Purchase #7 $231.50   4.291%   $241.4337   $241.43   $241.45   $241.40  
  7 purchase totals = $904.51       $984.3759   $984.37   $984.35   $984.40