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 $188.82   4.158%   $196.6711   $196.67   $196.65   $196.70  
  Purchase #2 $194.48   5.582%   $205.3359   $205.34   $205.35   $205.30  
  Purchase #3 $249.42   7.648%   $268.4956   $268.50   $268.50   $268.50  
  Purchase #4 $134.30   12.261%   $150.7665   $150.77   $150.75   $150.80  
  Purchase #5 $132.28   9.430%   $144.754   $144.75   $144.75   $144.80  
  Purchase #6 $67.40   10.369%   $74.3887   $74.39   $74.40   $74.40  
  Purchase #7 $21.64   8.711%   $23.5251   $23.53   $23.55   $23.50  
  7 purchase totals = $988.34       $1,063.9369   $1,063.95   $1,063.95   $1,064.00