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 $226.26   9.624%   $248.0353   $248.04   $248.05   $248.00  
  Purchase #2 $224.35   7.453%   $241.0708   $241.07   $241.05   $241.10  
  Purchase #3 $10.92   3.209%   $11.2704   $11.27   $11.25   $11.30  
  Purchase #4 $208.34   13.198%   $235.8367   $235.84   $235.85   $235.80  
  Purchase #5 $11.86   12.862%   $13.3854   $13.39   $13.40   $13.40  
  Purchase #6 $66.26   7.568%   $71.2746   $71.27   $71.25   $71.30  
  Purchase #7 $194.75   5.431%   $205.3269   $205.33   $205.35   $205.30  
  7 purchase totals = $942.74       $1,026.2001   $1,026.21   $1,026.20   $1,026.20