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 $186.95   6.232%   $198.6007   $198.60   $198.60   $198.60  
  Purchase #2 $177.71   9.472%   $194.5427   $194.54   $194.55   $194.50  
  Purchase #3 $166.56   6.518%   $177.4164   $177.42   $177.40   $177.40  
  Purchase #4 $60.87   4.320%   $63.4996   $63.50   $63.50   $63.50  
  Purchase #5 $10.91   9.145%   $11.9077   $11.91   $11.90   $11.90  
  Purchase #6 $24.93   3.570%   $25.82   $25.82   $25.80   $25.80  
  Purchase #7 $35.61   9.214%   $38.8911   $38.89   $38.90   $38.90  
  7 purchase totals = $663.54       $710.6782   $710.68   $710.65   $710.60