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 $19.64   4.645%   $20.5523   $20.55   $20.55   $20.60  
  Purchase #2 $212.37   7.254%   $227.7753   $227.78   $227.80   $227.80  
  Purchase #3 $68.39   8.175%   $73.9809   $73.98   $74.00   $74.00  
  Purchase #4 $20.64   4.285%   $21.5244   $21.52   $21.50   $21.50  
  Purchase #5 $94.75   13.308%   $107.3593   $107.36   $107.35   $107.40  
  Purchase #6 $197.25   11.450%   $219.8351   $219.84   $219.85   $219.80  
  Purchase #7 $205.33   7.549%   $220.8304   $220.83   $220.85   $220.80  
  7 purchase totals = $818.37       $891.8577   $891.86   $891.90   $891.90