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 $239.59   7.764%   $258.1918   $258.19   $258.20   $258.20  
  Purchase #2 $196.43   10.489%   $217.0335   $217.03   $217.05   $217.00  
  Purchase #3 $186.32   9.219%   $203.4968   $203.50   $203.50   $203.50  
  Purchase #4 $59.36   13.831%   $67.5701   $67.57   $67.55   $67.60  
  Purchase #5 $88.92   7.439%   $95.5348   $95.53   $95.55   $95.50  
  Purchase #6 $215.97   7.761%   $232.7314   $232.73   $232.75   $232.70  
  Purchase #7 $66.53   13.800%   $75.7111   $75.71   $75.70   $75.70  
  7 purchase totals = $1,053.12       $1,150.2695   $1,150.26   $1,150.30   $1,150.20