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 $208.47   13.765%   $237.1659   $237.17   $237.15   $237.20  
  Purchase #2 $56.65   7.718%   $61.0222   $61.02   $61.00   $61.00  
  Purchase #3 $161.41   8.312%   $174.8264   $174.83   $174.85   $174.80  
  Purchase #4 $6.66   4.139%   $6.9357   $6.94   $6.95   $6.90  
  Purchase #5 $197.96   8.635%   $215.0538   $215.05   $215.05   $215.10  
  Purchase #6 $223.50   11.785%   $249.8395   $249.84   $249.85   $249.80  
  Purchase #7 $105.76   13.485%   $120.0217   $120.02   $120.00   $120.00  
  7 purchase totals = $960.41       $1,064.8652   $1,064.87   $1,064.85   $1,064.80