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 $105.94   11.526%   $118.1506   $118.15   $118.15   $118.20  
  Purchase #2 $250.38   7.369%   $268.8305   $268.83   $268.85   $268.80  
  Purchase #3 $70.26   5.436%   $74.0793   $74.08   $74.10   $74.10  
  Purchase #4 $170.74   8.250%   $184.8261   $184.83   $184.85   $184.80  
  Purchase #5 $248.74   9.336%   $271.9624   $271.96   $271.95   $272.00  
  Purchase #6 $245.93   8.513%   $266.866   $266.87   $266.85   $266.90  
  Purchase #7 $113.62   8.564%   $123.3504   $123.35   $123.35   $123.40  
  7 purchase totals = $1,205.61       $1,308.0653   $1,308.07   $1,308.10   $1,308.20