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 $224.54   6.763%   $239.7256   $239.73   $239.75   $239.70  
  Purchase #2 $158.64   10.645%   $175.5272   $175.53   $175.55   $175.50  
  Purchase #3 $60.57   5.862%   $64.1206   $64.12   $64.10   $64.10  
  Purchase #4 $239.80   10.593%   $265.202   $265.20   $265.20   $265.20  
  Purchase #5 $218.42   6.367%   $232.3268   $232.33   $232.35   $232.30  
  Purchase #6 $101.92   3.767%   $105.7593   $105.76   $105.75   $105.80  
  Purchase #7 $238.72   5.148%   $251.0093   $251.01   $251.00   $251.00  
  7 purchase totals = $1,242.61       $1,333.6708   $1,333.68   $1,333.70   $1,333.60