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 $130.43   8.180%   $141.0992   $141.10   $141.10   $141.10  
  Purchase #2 $177.57   4.563%   $185.6725   $185.67   $185.65   $185.70  
  Purchase #3 $81.63   12.855%   $92.1235   $92.12   $92.10   $92.10  
  Purchase #4 $179.89   7.272%   $192.9716   $192.97   $192.95   $193.00  
  Purchase #5 $244.55   13.398%   $277.3148   $277.31   $277.30   $277.30  
  Purchase #6 $208.74   12.176%   $234.1562   $234.16   $234.15   $234.20  
  Purchase #7 $238.71   13.787%   $271.6209   $271.62   $271.60   $271.60  
  7 purchase totals = $1,261.52       $1,394.9587   $1,394.95   $1,394.85   $1,395.00