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 $107.36   11.128%   $119.307   $119.31   $119.30   $119.30  
  Purchase #2 $79.97   7.431%   $85.9126   $85.91   $85.90   $85.90  
  Purchase #3 $34.37   13.739%   $39.0921   $39.09   $39.10   $39.10  
  Purchase #4 $192.33   5.625%   $203.1486   $203.15   $203.15   $203.10  
  Purchase #5 $173.75   6.235%   $184.5833   $184.58   $184.60   $184.60  
  Purchase #6 $222.56   12.759%   $250.9564   $250.96   $250.95   $251.00  
  Purchase #7 $183.30   8.174%   $198.2829   $198.28   $198.30   $198.30  
  7 purchase totals = $993.64       $1,081.2829   $1,081.28   $1,081.30   $1,081.30