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 $204.53   11.488%   $228.0264   $228.03   $228.05   $228.00  
  Purchase #2 $184.71   10.350%   $203.8275   $203.83   $203.85   $203.80  
  Purchase #3 $119.27   5.635%   $125.9909   $125.99   $126.00   $126.00  
  Purchase #4 $9.54   11.508%   $10.6379   $10.64   $10.65   $10.60  
  Purchase #5 $103.45   3.831%   $107.4132   $107.41   $107.40   $107.40  
  Purchase #6 $11.78   8.310%   $12.7589   $12.76   $12.75   $12.80  
  Purchase #7 $44.42   12.759%   $50.0875   $50.09   $50.10   $50.10  
  7 purchase totals = $677.70       $738.7423   $738.75   $738.80   $738.70