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 $187.61   4.762%   $196.544   $196.54   $196.55   $196.50  
  Purchase #2 $67.26   3.773%   $69.7977   $69.80   $69.80   $69.80  
  Purchase #3 $242.78   11.394%   $270.4424   $270.44   $270.45   $270.40  
  Purchase #4 $249.90   5.696%   $264.1343   $264.13   $264.15   $264.10  
  Purchase #5 $27.30   4.823%   $28.6167   $28.62   $28.60   $28.60  
  Purchase #6 $141.59   5.846%   $149.8674   $149.87   $149.85   $149.90  
  Purchase #7 $212.61   13.418%   $241.138   $241.14   $241.15   $241.10  
  7 purchase totals = $1,129.05       $1,220.5405   $1,220.54   $1,220.55   $1,220.40