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 $69.91   5.473%   $73.7362   $73.74   $73.75   $73.70  
  Purchase #2 $195.60   5.763%   $206.8724   $206.87   $206.85   $206.90  
  Purchase #3 $130.39   3.753%   $135.2835   $135.28   $135.30   $135.30  
  Purchase #4 $164.31   11.236%   $182.7719   $182.77   $182.75   $182.80  
  Purchase #5 $178.32   11.315%   $198.4969   $198.50   $198.50   $198.50  
  Purchase #6 $199.87   12.381%   $224.6159   $224.62   $224.60   $224.60  
  Purchase #7 $64.72   3.423%   $66.9354   $66.94   $66.95   $66.90  
  7 purchase totals = $1,003.12       $1,088.7122   $1,088.72   $1,088.70   $1,088.70