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 $68.86   6.200%   $73.1293   $73.13   $73.15   $73.10  
  Purchase #2 $138.87   3.265%   $143.4041   $143.40   $143.40   $143.40  
  Purchase #3 $213.68   12.503%   $240.3964   $240.40   $240.40   $240.40  
  Purchase #4 $65.85   4.317%   $68.6927   $68.69   $68.70   $68.70  
  Purchase #5 $220.26   10.473%   $243.3278   $243.33   $243.35   $243.30  
  Purchase #6 $159.50   10.574%   $176.3655   $176.37   $176.35   $176.40  
  Purchase #7 $84.76   12.353%   $95.2304   $95.23   $95.25   $95.20  
  7 purchase totals = $951.78       $1,040.5462   $1,040.55   $1,040.60   $1,040.50