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 $63.93   9.467%   $69.9823   $69.98   $70.00   $70.00  
  Purchase #2 $208.88   13.261%   $236.5796   $236.58   $236.60   $236.60  
  Purchase #3 $104.69   6.576%   $111.5744   $111.57   $111.55   $111.60  
  Purchase #4 $212.67   11.166%   $236.4167   $236.42   $236.40   $236.40  
  Purchase #5 $62.64   5.113%   $65.8428   $65.84   $65.85   $65.80  
  Purchase #6 $103.44   9.201%   $112.9575   $112.96   $112.95   $113.00  
  Purchase #7 $99.87   6.623%   $106.4844   $106.48   $106.50   $106.50  
  7 purchase totals = $856.12       $939.8377   $939.83   $939.85   $939.90