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 $67.82   12.828%   $76.5199   $76.52   $76.50   $76.50  
  Purchase #2 $200.93   6.192%   $213.3716   $213.37   $213.35   $213.40  
  Purchase #3 $70.93   6.423%   $75.4858   $75.49   $75.50   $75.50  
  Purchase #4 $30.49   8.110%   $32.9627   $32.96   $32.95   $33.00  
  Purchase #5 $219.71   4.790%   $230.2341   $230.23   $230.25   $230.20  
  Purchase #6 $167.98   10.342%   $185.3525   $185.35   $185.35   $185.40  
  Purchase #7 $73.32   5.444%   $77.3115   $77.31   $77.30   $77.30  
  7 purchase totals = $831.18       $891.2381   $891.23   $891.20   $891.30