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 $31.40   12.671%   $35.3787   $35.38   $35.40   $35.40  
  Purchase #2 $222.90   9.442%   $243.9462   $243.95   $243.95   $243.90  
  Purchase #3 $124.72   9.172%   $136.1593   $136.16   $136.15   $136.20  
  Purchase #4 $188.37   8.160%   $203.741   $203.74   $203.75   $203.70  
  Purchase #5 $107.99   5.338%   $113.7545   $113.75   $113.75   $113.80  
  Purchase #6 $46.99   6.262%   $49.9325   $49.93   $49.95   $49.90  
  Purchase #7 $240.85   3.257%   $248.6945   $248.69   $248.70   $248.70  
  7 purchase totals = $963.22       $1,031.6067   $1,031.60   $1,031.65   $1,031.60