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 $214.97   12.178%   $241.149   $241.15   $241.15   $241.10  
  Purchase #2 $39.82   9.873%   $43.7514   $43.75   $43.75   $43.80  
  Purchase #3 $126.29   12.309%   $141.835   $141.84   $141.85   $141.80  
  Purchase #4 $226.28   8.377%   $245.2355   $245.24   $245.25   $245.20  
  Purchase #5 $70.51   5.628%   $74.4783   $74.48   $74.50   $74.50  
  Purchase #6 $250.34   3.632%   $259.4323   $259.43   $259.45   $259.40  
  Purchase #7 $11.26   11.201%   $12.5212   $12.52   $12.50   $12.50  
  7 purchase totals = $939.47       $1,018.4027   $1,018.41   $1,018.45   $1,018.30