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 $185.75   6.519%   $197.859   $197.86   $197.85   $197.90  
  Purchase #2 $150.88   3.279%   $155.8274   $155.83   $155.85   $155.80  
  Purchase #3 $23.29   9.852%   $25.5845   $25.58   $25.60   $25.60  
  Purchase #4 $89.30   5.697%   $94.3874   $94.39   $94.40   $94.40  
  Purchase #5 $104.28   5.667%   $110.1895   $110.19   $110.20   $110.20  
  Purchase #6 $64.90   3.810%   $67.3727   $67.37   $67.35   $67.40  
  Purchase #7 $133.44   9.565%   $146.2035   $146.20   $146.20   $146.20  
  7 purchase totals = $751.84       $797.4240   $797.42   $797.45   $797.50