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 $218.62   6.809%   $233.5058   $233.51   $233.50   $233.50  
  Purchase #2 $31.37   9.327%   $34.2959   $34.30   $34.30   $34.30  
  Purchase #3 $62.64   9.104%   $68.3427   $68.34   $68.35   $68.30  
  Purchase #4 $237.78   7.714%   $256.1223   $256.12   $256.10   $256.10  
  Purchase #5 $35.80   12.859%   $40.4035   $40.40   $40.40   $40.40  
  Purchase #6 $187.87   9.592%   $205.8905   $205.89   $205.90   $205.90  
  Purchase #7 $177.34   5.331%   $186.794   $186.79   $186.80   $186.80  
  7 purchase totals = $951.42       $1,025.3547   $1,025.35   $1,025.35   $1,025.30