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 $54.28   11.287%   $60.4066   $60.41   $60.40   $60.40  
  Purchase #2 $157.72   10.540%   $174.3437   $174.34   $174.35   $174.30  
  Purchase #3 $42.28   6.184%   $44.8946   $44.89   $44.90   $44.90  
  Purchase #4 $162.39   9.805%   $178.3123   $178.31   $178.30   $178.30  
  Purchase #5 $169.78   7.784%   $182.9957   $183.00   $183.00   $183.00  
  Purchase #6 $169.44   7.197%   $181.6346   $181.63   $181.65   $181.60  
  Purchase #7 $222.25   4.707%   $232.7113   $232.71   $232.70   $232.70  
  7 purchase totals = $978.14       $1,055.2988   $1,055.29   $1,055.30   $1,055.20