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 $202.86   10.432%   $224.0224   $224.02   $224.00   $224.00  
  Purchase #2 $43.96   6.535%   $46.8328   $46.83   $46.85   $46.80  
  Purchase #3 $191.39   13.838%   $217.8745   $217.87   $217.85   $217.90  
  Purchase #4 $220.36   4.666%   $230.642   $230.64   $230.65   $230.60  
  Purchase #5 $209.99   7.127%   $224.956   $224.96   $224.95   $225.00  
  Purchase #6 $41.73   6.522%   $44.4516   $44.45   $44.45   $44.50  
  Purchase #7 $129.78   7.628%   $139.6796   $139.68   $139.70   $139.70  
  7 purchase totals = $1,040.07       $1,128.4589   $1,128.45   $1,128.45   $1,128.50