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 $237.96   12.612%   $267.9715   $267.97   $267.95   $268.00  
  Purchase #2 $83.78   4.847%   $87.8408   $87.84   $87.85   $87.80  
  Purchase #3 $172.91   11.749%   $193.2252   $193.23   $193.25   $193.20  
  Purchase #4 $51.87   9.175%   $56.6291   $56.63   $56.65   $56.60  
  Purchase #5 $18.90   9.407%   $20.6779   $20.68   $20.70   $20.70  
  Purchase #6 $235.65   7.602%   $253.5641   $253.56   $253.55   $253.60  
  Purchase #7 $120.96   10.854%   $134.089   $134.09   $134.10   $134.10  
  7 purchase totals = $922.03       $1,013.9976   $1,014.00   $1,014.05   $1,014.00