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 $28.34   9.669%   $31.0802   $31.08   $31.10   $31.10  
  Purchase #2 $13.25   3.815%   $13.7555   $13.76   $13.75   $13.80  
  Purchase #3 $194.57   9.583%   $213.2156   $213.22   $213.20   $213.20  
  Purchase #4 $42.89   7.774%   $46.2243   $46.22   $46.20   $46.20  
  Purchase #5 $40.98   9.532%   $44.8862   $44.89   $44.90   $44.90  
  Purchase #6 $146.70   13.385%   $166.3358   $166.34   $166.35   $166.30  
  Purchase #7 $132.50   12.113%   $148.5497   $148.55   $148.55   $148.50  
  7 purchase totals = $599.23       $664.0473   $664.06   $664.05   $664.00