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 $66.58   6.491%   $70.9017   $70.90   $70.90   $70.90  
  Purchase #2 $187.61   9.463%   $205.3635   $205.36   $205.35   $205.40  
  Purchase #3 $160.43   7.628%   $172.6676   $172.67   $172.65   $172.70  
  Purchase #4 $36.63   7.129%   $39.2414   $39.24   $39.25   $39.20  
  Purchase #5 $90.84   4.596%   $95.015   $95.02   $95.00   $95.00  
  Purchase #6 $111.63   7.756%   $120.288   $120.29   $120.30   $120.30  
  Purchase #7 $163.85   10.145%   $180.4726   $180.47   $180.45   $180.50  
  7 purchase totals = $817.57       $883.9498   $883.95   $883.90   $884.00