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 $114.34   3.176%   $117.9714   $117.97   $117.95   $118.00  
  Purchase #2 $60.35   8.194%   $65.2951   $65.30   $65.30   $65.30  
  Purchase #3 $106.83   5.678%   $112.8958   $112.90   $112.90   $112.90  
  Purchase #4 $205.62   10.152%   $226.4945   $226.49   $226.50   $226.50  
  Purchase #5 $10.75   5.121%   $11.3005   $11.30   $11.30   $11.30  
  Purchase #6 $244.57   8.159%   $264.5245   $264.52   $264.50   $264.50  
  Purchase #7 $213.27   13.123%   $241.2574   $241.26   $241.25   $241.30  
  7 purchase totals = $955.73       $1,039.7392   $1,039.74   $1,039.70   $1,039.80