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 $109.93   12.829%   $124.0329   $124.03   $124.05   $124.00  
  Purchase #2 $163.93   10.641%   $181.3738   $181.37   $181.35   $181.40  
  Purchase #3 $241.58   13.538%   $274.2851   $274.29   $274.30   $274.30  
  Purchase #4 $152.65   3.516%   $158.0172   $158.02   $158.00   $158.00  
  Purchase #5 $195.89   4.289%   $204.2917   $204.29   $204.30   $204.30  
  Purchase #6 $167.54   5.235%   $176.3107   $176.31   $176.30   $176.30  
  Purchase #7 $188.31   9.607%   $206.4009   $206.40   $206.40   $206.40  
  7 purchase totals = $1,219.83       $1,324.7123   $1,324.71   $1,324.70   $1,324.70