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 $181.26   8.867%   $197.3323   $197.33   $197.35   $197.30  
  Purchase #2 $121.95   11.858%   $136.4108   $136.41   $136.40   $136.40  
  Purchase #3 $154.70   3.596%   $160.263   $160.26   $160.25   $160.30  
  Purchase #4 $204.36   4.393%   $213.3375   $213.34   $213.35   $213.30  
  Purchase #5 $216.31   13.264%   $245.0014   $245.00   $245.00   $245.00  
  Purchase #6 $38.26   6.304%   $40.6719   $40.67   $40.65   $40.70  
  Purchase #7 $73.47   3.697%   $76.1862   $76.19   $76.20   $76.20  
  7 purchase totals = $990.31       $1,069.2031   $1,069.20   $1,069.20   $1,069.20