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 $232.35   3.726%   $241.0074   $241.01   $241.00   $241.00  
  Purchase #2 $93.55   7.473%   $100.541   $100.54   $100.55   $100.50  
  Purchase #3 $193.37   6.459%   $205.8598   $205.86   $205.85   $205.90  
  Purchase #4 $64.27   5.508%   $67.81   $67.81   $67.80   $67.80  
  Purchase #5 $190.48   5.555%   $201.0612   $201.06   $201.05   $201.10  
  Purchase #6 $62.30   8.677%   $67.7058   $67.71   $67.70   $67.70  
  Purchase #7 $232.44   7.361%   $249.5499   $249.55   $249.55   $249.50  
  7 purchase totals = $1,068.76       $1,133.5351   $1,133.54   $1,133.50   $1,133.50