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 $240.91   10.853%   $267.056   $267.06   $267.05   $267.10  
  Purchase #2 $249.59   10.172%   $274.9783   $274.98   $275.00   $275.00  
  Purchase #3 $71.80   4.467%   $75.0073   $75.01   $75.00   $75.00  
  Purchase #4 $222.55   13.169%   $251.8576   $251.86   $251.85   $251.90  
  Purchase #5 $127.98   3.799%   $132.842   $132.84   $132.85   $132.80  
  Purchase #6 $241.43   6.635%   $257.4489   $257.45   $257.45   $257.40  
  Purchase #7 $180.97   3.663%   $187.5989   $187.60   $187.60   $187.60  
  7 purchase totals = $1,335.23       $1,446.7890   $1,446.80   $1,446.80   $1,446.80