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 $219.89   8.345%   $238.2398   $238.24   $238.25   $238.20  
  Purchase #2 $98.58   12.147%   $110.5545   $110.55   $110.55   $110.60  
  Purchase #3 $26.90   12.318%   $30.2135   $30.21   $30.20   $30.20  
  Purchase #4 $207.26   12.816%   $233.8224   $233.82   $233.80   $233.80  
  Purchase #5 $167.30   3.605%   $173.3312   $173.33   $173.35   $173.30  
  Purchase #6 $136.42   9.592%   $149.5054   $149.51   $149.50   $149.50  
  Purchase #7 $164.49   3.686%   $170.5531   $170.55   $170.55   $170.60  
  7 purchase totals = $1,020.84       $1,106.2199   $1,106.21   $1,106.20   $1,106.20