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 $83.75   6.225%   $88.9634   $88.96   $88.95   $89.00  
  Purchase #2 $244.86   13.470%   $277.8426   $277.84   $277.85   $277.80  
  Purchase #3 $149.58   11.258%   $166.4197   $166.42   $166.40   $166.40  
  Purchase #4 $19.30   6.629%   $20.5794   $20.58   $20.60   $20.60  
  Purchase #5 $237.51   3.540%   $245.9179   $245.92   $245.90   $245.90  
  Purchase #6 $192.81   7.206%   $206.7039   $206.70   $206.70   $206.70  
  Purchase #7 $235.92   5.708%   $249.3863   $249.39   $249.40   $249.40  
  7 purchase totals = $1,163.73       $1,255.8132   $1,255.81   $1,255.80   $1,255.80