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 $89.45   7.546%   $96.1999   $96.20   $96.20   $96.20  
  Purchase #2 $148.95   5.305%   $156.8518   $156.85   $156.85   $156.90  
  Purchase #3 $107.47   12.560%   $120.9682   $120.97   $120.95   $121.00  
  Purchase #4 $110.90   6.254%   $117.8357   $117.84   $117.85   $117.80  
  Purchase #5 $40.74   8.661%   $44.2685   $44.27   $44.25   $44.30  
  Purchase #6 $191.35   11.434%   $213.229   $213.23   $213.25   $213.20  
  Purchase #7 $213.76   10.394%   $235.9782   $235.98   $236.00   $236.00  
  7 purchase totals = $902.62       $985.3313   $985.34   $985.35   $985.40