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 $119.34   9.392%   $130.5484   $130.55   $130.55   $130.50  
  Purchase #2 $185.87   3.629%   $192.6152   $192.62   $192.60   $192.60  
  Purchase #3 $196.65   3.399%   $203.3341   $203.33   $203.35   $203.30  
  Purchase #4 $59.59   8.515%   $64.6641   $64.66   $64.65   $64.70  
  Purchase #5 $208.86   9.584%   $228.8771   $228.88   $228.90   $228.90  
  Purchase #6 $180.89   7.473%   $194.4079   $194.41   $194.40   $194.40  
  Purchase #7 $142.70   4.545%   $149.1857   $149.19   $149.20   $149.20  
  7 purchase totals = $1,093.90       $1,163.6325   $1,163.64   $1,163.65   $1,163.60