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 $175.61   11.155%   $195.1993   $195.20   $195.20   $195.20  
  Purchase #2 $93.45   11.522%   $104.2173   $104.22   $104.20   $104.20  
  Purchase #3 $64.57   13.701%   $73.4167   $73.42   $73.40   $73.40  
  Purchase #4 $207.68   7.797%   $223.8728   $223.87   $223.85   $223.90  
  Purchase #5 $61.30   6.317%   $65.1723   $65.17   $65.15   $65.20  
  Purchase #6 $58.67   9.565%   $64.2818   $64.28   $64.30   $64.30  
  Purchase #7 $12.68   7.174%   $13.5897   $13.59   $13.60   $13.60  
  7 purchase totals = $673.96       $739.7499   $739.75   $739.70   $739.80