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 $218.32   7.572%   $234.8512   $234.85   $234.85   $234.90  
  Purchase #2 $167.56   7.228%   $179.6712   $179.67   $179.65   $179.70  
  Purchase #3 $248.68   10.819%   $275.5847   $275.58   $275.60   $275.60  
  Purchase #4 $87.66   9.400%   $95.9   $95.90   $95.90   $95.90  
  Purchase #5 $173.29   11.436%   $193.1074   $193.11   $193.10   $193.10  
  Purchase #6 $119.26   4.446%   $124.5623   $124.56   $124.55   $124.60  
  Purchase #7 $208.98   3.209%   $215.6862   $215.69   $215.70   $215.70  
  7 purchase totals = $1,223.75       $1,319.3630   $1,319.36   $1,319.35   $1,319.50