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 $191.47   7.219%   $205.2922   $205.29   $205.30   $205.30  
  Purchase #2 $119.79   5.202%   $126.0215   $126.02   $126.00   $126.00  
  Purchase #3 $198.63   10.400%   $219.2875   $219.29   $219.30   $219.30  
  Purchase #4 $211.37   11.436%   $235.5423   $235.54   $235.55   $235.50  
  Purchase #5 $80.67   7.169%   $86.4532   $86.45   $86.45   $86.50  
  Purchase #6 $85.80   12.649%   $96.6528   $96.65   $96.65   $96.70  
  Purchase #7 $12.26   11.464%   $13.6655   $13.67   $13.65   $13.70  
  7 purchase totals = $899.99       $982.9150   $982.91   $982.90   $983.00