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 $208.89   12.116%   $234.1991   $234.20   $234.20   $234.20  
  Purchase #2 $147.29   3.861%   $152.9769   $152.98   $153.00   $153.00  
  Purchase #3 $84.66   10.497%   $93.5468   $93.55   $93.55   $93.50  
  Purchase #4 $219.90   5.168%   $231.2644   $231.26   $231.25   $231.30  
  Purchase #5 $244.48   6.152%   $259.5204   $259.52   $259.50   $259.50  
  Purchase #6 $133.79   11.333%   $148.9524   $148.95   $148.95   $149.00  
  Purchase #7 $221.68   11.353%   $246.8473   $246.85   $246.85   $246.80  
  7 purchase totals = $1,260.69       $1,367.3073   $1,367.31   $1,367.30   $1,367.30