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 $189.79   6.335%   $201.8132   $201.81   $201.80   $201.80  
  Purchase #2 $22.63   13.248%   $25.628   $25.63   $25.65   $25.60  
  Purchase #3 $83.60   5.169%   $87.9213   $87.92   $87.90   $87.90  
  Purchase #4 $53.53   6.690%   $57.1112   $57.11   $57.10   $57.10  
  Purchase #5 $86.27   8.569%   $93.6625   $93.66   $93.65   $93.70  
  Purchase #6 $53.53   5.607%   $56.5314   $56.53   $56.55   $56.50  
  Purchase #7 $242.96   3.566%   $251.624   $251.62   $251.60   $251.60  
  7 purchase totals = $732.31       $774.2916   $774.28   $774.25   $774.20