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 $175.71   7.137%   $188.2504   $188.25   $188.25   $188.30  
  Purchase #2 $104.92   8.816%   $114.1697   $114.17   $114.15   $114.20  
  Purchase #3 $48.94   6.219%   $51.9836   $51.98   $52.00   $52.00  
  Purchase #4 $140.64   13.161%   $159.1496   $159.15   $159.15   $159.10  
  Purchase #5 $83.59   7.663%   $89.9955   $90.00   $90.00   $90.00  
  Purchase #6 $162.32   13.819%   $184.751   $184.75   $184.75   $184.80  
  Purchase #7 $232.58   6.116%   $246.8046   $246.80   $246.80   $246.80  
  7 purchase totals = $948.70       $1,035.1044   $1,035.10   $1,035.10   $1,035.20