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 $193.30   6.661%   $206.1757   $206.18   $206.20   $206.20  
  Purchase #2 $67.71   5.826%   $71.6548   $71.65   $71.65   $71.70  
  Purchase #3 $192.62   8.559%   $209.1063   $209.11   $209.10   $209.10  
  Purchase #4 $45.99   8.185%   $49.7543   $49.75   $49.75   $49.80  
  Purchase #5 $238.43   6.658%   $254.3047   $254.30   $254.30   $254.30  
  Purchase #6 $109.31   9.611%   $119.8158   $119.82   $119.80   $119.80  
  Purchase #7 $35.37   6.794%   $37.773   $37.77   $37.75   $37.80  
  7 purchase totals = $882.73       $948.5846   $948.58   $948.55   $948.70