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 $194.33   5.624%   $205.2591   $205.26   $205.25   $205.30  
  Purchase #2 $172.62   10.199%   $190.2255   $190.23   $190.25   $190.20  
  Purchase #3 $215.29   7.116%   $230.61   $230.61   $230.60   $230.60  
  Purchase #4 $86.78   9.108%   $94.6839   $94.68   $94.70   $94.70  
  Purchase #5 $28.51   9.369%   $31.1811   $31.18   $31.20   $31.20  
  Purchase #6 $245.58   3.781%   $254.8654   $254.87   $254.85   $254.90  
  Purchase #7 $241.25   11.497%   $268.9865   $268.99   $269.00   $269.00  
  7 purchase totals = $1,184.36       $1,275.8115   $1,275.82   $1,275.85   $1,275.90