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 $60.64   3.660%   $62.8594   $62.86   $62.85   $62.90  
  Purchase #2 $142.35   12.151%   $159.6469   $159.65   $159.65   $159.60  
  Purchase #3 $86.47   11.481%   $96.3976   $96.40   $96.40   $96.40  
  Purchase #4 $186.54   9.339%   $203.961   $203.96   $203.95   $204.00  
  Purchase #5 $75.90   8.554%   $82.3925   $82.39   $82.40   $82.40  
  Purchase #6 $84.90   10.196%   $93.5564   $93.56   $93.55   $93.60  
  Purchase #7 $227.75   12.539%   $256.3076   $256.31   $256.30   $256.30  
  7 purchase totals = $864.55       $955.1214   $955.13   $955.10   $955.20