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 $71.79   7.463%   $77.1477   $77.15   $77.15   $77.10  
  Purchase #2 $147.25   10.591%   $162.8452   $162.85   $162.85   $162.80  
  Purchase #3 $250.81   5.337%   $264.1957   $264.20   $264.20   $264.20  
  Purchase #4 $82.47   11.387%   $91.8609   $91.86   $91.85   $91.90  
  Purchase #5 $174.71   13.574%   $198.4251   $198.43   $198.45   $198.40  
  Purchase #6 $72.96   4.564%   $76.2899   $76.29   $76.30   $76.30  
  Purchase #7 $12.86   10.410%   $14.1987   $14.20   $14.20   $14.20  
  7 purchase totals = $812.85       $884.9632   $884.98   $885.00   $884.90