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 $85.35   12.781%   $96.2586   $96.26   $96.25   $96.30  
  Purchase #2 $89.79   4.236%   $93.5935   $93.59   $93.60   $93.60  
  Purchase #3 $152.81   7.199%   $163.8108   $163.81   $163.80   $163.80  
  Purchase #4 $135.39   4.748%   $141.8183   $141.82   $141.80   $141.80  
  Purchase #5 $191.71   11.188%   $213.1585   $213.16   $213.15   $213.20  
  Purchase #6 $152.54   4.254%   $159.0291   $159.03   $159.05   $159.00  
  Purchase #7 $87.28   6.594%   $93.0352   $93.04   $93.05   $93.00  
  7 purchase totals = $894.87       $960.7040   $960.71   $960.70   $960.70