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 $245.33   9.617%   $268.9234   $268.92   $268.90   $268.90  
  Purchase #2 $126.29   12.332%   $141.8641   $141.86   $141.85   $141.90  
  Purchase #3 $100.52   8.761%   $109.3266   $109.33   $109.35   $109.30  
  Purchase #4 $245.56   13.563%   $278.8653   $278.87   $278.85   $278.90  
  Purchase #5 $239.49   4.224%   $249.6061   $249.61   $249.60   $249.60  
  Purchase #6 $188.46   13.109%   $213.1652   $213.17   $213.15   $213.20  
  Purchase #7 $89.97   5.411%   $94.8383   $94.84   $94.85   $94.80  
  7 purchase totals = $1,235.62       $1,356.5890   $1,356.60   $1,356.55   $1,356.60