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 $138.78   10.427%   $153.2506   $153.25   $153.25   $153.30  
  Purchase #2 $221.55   6.691%   $236.3739   $236.37   $236.35   $236.40  
  Purchase #3 $60.25   3.485%   $62.3497   $62.35   $62.35   $62.30  
  Purchase #4 $177.56   3.349%   $183.5065   $183.51   $183.50   $183.50  
  Purchase #5 $210.95   13.520%   $239.4704   $239.47   $239.45   $239.50  
  Purchase #6 $204.47   6.735%   $218.2411   $218.24   $218.25   $218.20  
  Purchase #7 $55.65   6.344%   $59.1804   $59.18   $59.20   $59.20  
  7 purchase totals = $1,069.21       $1,152.3726   $1,152.37   $1,152.35   $1,152.40