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 $142.49   13.444%   $161.6464   $161.65   $161.65   $161.60  
  Purchase #2 $152.54   3.293%   $157.5631   $157.56   $157.55   $157.60  
  Purchase #3 $57.44   11.771%   $64.2013   $64.20   $64.20   $64.20  
  Purchase #4 $214.36   4.658%   $224.3449   $224.34   $224.35   $224.30  
  Purchase #5 $221.74   9.481%   $242.7632   $242.76   $242.75   $242.80  
  Purchase #6 $39.89   13.340%   $45.2113   $45.21   $45.20   $45.20  
  Purchase #7 $116.43   6.359%   $123.8338   $123.83   $123.85   $123.80  
  7 purchase totals = $944.89       $1,019.5640   $1,019.55   $1,019.55   $1,019.50