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 $209.36   8.173%   $226.471   $226.47   $226.45   $226.50  
  Purchase #2 $84.45   13.634%   $95.9639   $95.96   $95.95   $96.00  
  Purchase #3 $183.52   11.687%   $204.968   $204.97   $204.95   $205.00  
  Purchase #4 $128.61   8.789%   $139.9135   $139.91   $139.90   $139.90  
  Purchase #5 $154.30   4.724%   $161.5891   $161.59   $161.60   $161.60  
  Purchase #6 $130.51   9.142%   $142.4412   $142.44   $142.45   $142.40  
  Purchase #7 $248.39   8.266%   $268.9219   $268.92   $268.90   $268.90  
  7 purchase totals = $1,139.14       $1,240.2686   $1,240.26   $1,240.20   $1,240.30