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 $227.76   6.681%   $242.9766   $242.98   $243.00   $243.00  
  Purchase #2 $8.57   7.111%   $9.1794   $9.18   $9.20   $9.20  
  Purchase #3 $217.42   6.554%   $231.6697   $231.67   $231.65   $231.70  
  Purchase #4 $234.32   12.627%   $263.9076   $263.91   $263.90   $263.90  
  Purchase #5 $199.67   13.519%   $226.6634   $226.66   $226.65   $226.70  
  Purchase #6 $170.31   3.664%   $176.5502   $176.55   $176.55   $176.60  
  Purchase #7 $113.38   6.291%   $120.5127   $120.51   $120.50   $120.50  
  7 purchase totals = $1,171.43       $1,271.4596   $1,271.46   $1,271.45   $1,271.60