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 $43.87   11.221%   $48.7927   $48.79   $48.80   $48.80  
  Purchase #2 $145.91   5.187%   $153.4784   $153.48   $153.50   $153.50  
  Purchase #3 $69.36   7.575%   $74.614   $74.61   $74.60   $74.60  
  Purchase #4 $43.64   6.697%   $46.5626   $46.56   $46.55   $46.60  
  Purchase #5 $53.92   9.605%   $59.099   $59.10   $59.10   $59.10  
  Purchase #6 $224.40   11.228%   $249.5956   $249.60   $249.60   $249.60  
  Purchase #7 $204.71   11.851%   $228.9702   $228.97   $228.95   $229.00  
  7 purchase totals = $785.81       $861.1125   $861.11   $861.10   $861.20