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 $56.97   8.844%   $62.0084   $62.01   $62.00   $62.00  
  Purchase #2 $170.43   6.195%   $180.9881   $180.99   $181.00   $181.00  
  Purchase #3 $5.69   4.395%   $5.9401   $5.94   $5.95   $5.90  
  Purchase #4 $61.33   8.104%   $66.3002   $66.30   $66.30   $66.30  
  Purchase #5 $12.74   9.845%   $13.9943   $13.99   $14.00   $14.00  
  Purchase #6 $235.56   13.415%   $267.1604   $267.16   $267.15   $267.20  
  Purchase #7 $212.72   10.632%   $235.3364   $235.34   $235.35   $235.30  
  7 purchase totals = $755.44       $831.7279   $831.73   $831.75   $831.70