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 $44.71   12.569%   $50.3296   $50.33   $50.35   $50.30  
  Purchase #2 $241.31   9.719%   $264.7629   $264.76   $264.75   $264.80  
  Purchase #3 $162.97   8.283%   $176.4688   $176.47   $176.45   $176.50  
  Purchase #4 $233.38   13.212%   $264.2142   $264.21   $264.20   $264.20  
  Purchase #5 $17.52   3.743%   $18.1758   $18.18   $18.20   $18.20  
  Purchase #6 $152.35   5.221%   $160.3042   $160.30   $160.30   $160.30  
  Purchase #7 $82.53   6.307%   $87.7352   $87.74   $87.75   $87.70  
  7 purchase totals = $934.77       $1,021.9907   $1,021.99   $1,022.00   $1,022.00