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 $141.84   8.826%   $154.3588   $154.36   $154.35   $154.40  
  Purchase #2 $25.37   4.194%   $26.434   $26.43   $26.45   $26.40  
  Purchase #3 $188.34   9.415%   $206.0722   $206.07   $206.05   $206.10  
  Purchase #4 $64.89   13.219%   $73.4678   $73.47   $73.45   $73.50  
  Purchase #5 $119.65   7.250%   $128.3246   $128.32   $128.30   $128.30  
  Purchase #6 $236.63   8.313%   $256.3011   $256.30   $256.30   $256.30  
  Purchase #7 $228.25   8.571%   $247.8133   $247.81   $247.80   $247.80  
  7 purchase totals = $1,004.97       $1,092.7718   $1,092.76   $1,092.70   $1,092.80