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 $218.31   4.199%   $227.4768   $227.48   $227.50   $227.50  
  Purchase #2 $190.97   3.492%   $197.6387   $197.64   $197.65   $197.60  
  Purchase #3 $70.48   13.592%   $80.0596   $80.06   $80.05   $80.10  
  Purchase #4 $209.66   5.803%   $221.8266   $221.83   $221.85   $221.80  
  Purchase #5 $169.65   12.359%   $190.617   $190.62   $190.60   $190.60  
  Purchase #6 $183.91   9.300%   $201.0136   $201.01   $201.00   $201.00  
  Purchase #7 $201.39   11.345%   $224.2377   $224.24   $224.25   $224.20  
  7 purchase totals = $1,244.37       $1,342.8700   $1,342.88   $1,342.90   $1,342.80