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 $85.79   10.869%   $95.1145   $95.11   $95.10   $95.10  
  Purchase #2 $178.74   5.133%   $187.9147   $187.91   $187.90   $187.90  
  Purchase #3 $83.59   12.361%   $93.9226   $93.92   $93.90   $93.90  
  Purchase #4 $182.97   10.691%   $202.5313   $202.53   $202.55   $202.50  
  Purchase #5 $152.41   6.649%   $162.5437   $162.54   $162.55   $162.50  
  Purchase #6 $106.67   13.296%   $120.8528   $120.85   $120.85   $120.90  
  Purchase #7 $150.99   5.869%   $159.8516   $159.85   $159.85   $159.90  
  7 purchase totals = $941.16       $1,022.7312   $1,022.71   $1,022.70   $1,022.70