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 $208.75   12.222%   $234.2634   $234.26   $234.25   $234.30  
  Purchase #2 $77.54   7.847%   $83.6246   $83.62   $83.60   $83.60  
  Purchase #3 $234.62   4.259%   $244.6125   $244.61   $244.60   $244.60  
  Purchase #4 $49.90   8.753%   $54.2677   $54.27   $54.25   $54.30  
  Purchase #5 $240.85   5.848%   $254.9349   $254.93   $254.95   $254.90  
  Purchase #6 $103.88   12.729%   $117.1029   $117.10   $117.10   $117.10  
  Purchase #7 $59.65   5.683%   $63.0399   $63.04   $63.05   $63.00  
  7 purchase totals = $975.19       $1,051.8459   $1,051.83   $1,051.80   $1,051.80