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 $83.97   5.691%   $88.7487   $88.75   $88.75   $88.70  
  Purchase #2 $226.25   11.272%   $251.7529   $251.75   $251.75   $251.80  
  Purchase #3 $13.40   4.826%   $14.0467   $14.05   $14.05   $14.00  
  Purchase #4 $250.94   6.578%   $267.4468   $267.45   $267.45   $267.40  
  Purchase #5 $120.47   10.787%   $133.4651   $133.47   $133.45   $133.50  
  Purchase #6 $221.48   8.298%   $239.8584   $239.86   $239.85   $239.90  
  Purchase #7 $150.44   9.156%   $164.2143   $164.21   $164.20   $164.20  
  7 purchase totals = $1,066.95       $1,159.5329   $1,159.54   $1,159.50   $1,159.50