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 $214.60   5.577%   $226.5682   $226.57   $226.55   $226.60  
  Purchase #2 $182.98   11.479%   $203.9843   $203.98   $204.00   $204.00  
  Purchase #3 $232.28   9.212%   $253.6776   $253.68   $253.70   $253.70  
  Purchase #4 $113.36   7.424%   $121.7758   $121.78   $121.80   $121.80  
  Purchase #5 $41.96   3.645%   $43.4894   $43.49   $43.50   $43.50  
  Purchase #6 $128.83   9.368%   $140.8988   $140.90   $140.90   $140.90  
  Purchase #7 $42.63   9.532%   $46.6935   $46.69   $46.70   $46.70  
  7 purchase totals = $956.64       $1,037.0876   $1,037.09   $1,037.15   $1,037.20