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 $246.70   8.740%   $268.2616   $268.26   $268.25   $268.30  
  Purchase #2 $92.67   4.660%   $96.9884   $96.99   $97.00   $97.00  
  Purchase #3 $205.68   9.869%   $225.9786   $225.98   $226.00   $226.00  
  Purchase #4 $130.65   8.662%   $141.9669   $141.97   $141.95   $142.00  
  Purchase #5 $60.29   3.385%   $62.3308   $62.33   $62.35   $62.30  
  Purchase #6 $7.39   11.641%   $8.2503   $8.25   $8.25   $8.30  
  Purchase #7 $190.90   7.689%   $205.5783   $205.58   $205.60   $205.60  
  7 purchase totals = $934.28       $1,009.3549   $1,009.36   $1,009.40   $1,009.50