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 $129.48   7.727%   $139.4849   $139.48   $139.50   $139.50  
  Purchase #2 $231.62   6.728%   $247.2034   $247.20   $247.20   $247.20  
  Purchase #3 $46.53   13.799%   $52.9507   $52.95   $52.95   $53.00  
  Purchase #4 $29.94   3.362%   $30.9466   $30.95   $30.95   $30.90  
  Purchase #5 $92.80   11.146%   $103.1435   $103.14   $103.15   $103.10  
  Purchase #6 $242.87   4.817%   $254.569   $254.57   $254.55   $254.60  
  Purchase #7 $107.71   11.148%   $119.7175   $119.72   $119.70   $119.70  
  7 purchase totals = $880.95       $948.0156   $948.01   $948.00   $948.00