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 $148.74   12.439%   $167.2418   $167.24   $167.25   $167.20  
  Purchase #2 $57.43   9.523%   $62.8991   $62.90   $62.90   $62.90  
  Purchase #3 $247.54   6.226%   $262.9518   $262.95   $262.95   $263.00  
  Purchase #4 $248.70   9.673%   $272.7568   $272.76   $272.75   $272.80  
  Purchase #5 $80.58   4.222%   $83.9821   $83.98   $84.00   $84.00  
  Purchase #6 $106.43   11.326%   $118.4843   $118.48   $118.50   $118.50  
  Purchase #7 $48.99   4.756%   $51.32   $51.32   $51.30   $51.30  
  7 purchase totals = $938.41       $1,019.6359   $1,019.63   $1,019.65   $1,019.70