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 $244.64   6.282%   $260.0083   $260.01   $260.00   $260.00  
  Purchase #2 $28.95   12.393%   $32.5378   $32.54   $32.55   $32.50  
  Purchase #3 $119.59   12.629%   $134.693   $134.69   $134.70   $134.70  
  Purchase #4 $247.65   13.324%   $280.6469   $280.65   $280.65   $280.60  
  Purchase #5 $106.28   11.774%   $118.7934   $118.79   $118.80   $118.80  
  Purchase #6 $47.89   10.532%   $52.9338   $52.93   $52.95   $52.90  
  Purchase #7 $131.30   10.591%   $145.206   $145.21   $145.20   $145.20  
  7 purchase totals = $926.30       $1,024.8192   $1,024.82   $1,024.85   $1,024.70