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 $68.76   9.561%   $75.3341   $75.33   $75.35   $75.30  
  Purchase #2 $101.61   13.827%   $115.6596   $115.66   $115.65   $115.70  
  Purchase #3 $118.75   4.498%   $124.0914   $124.09   $124.10   $124.10  
  Purchase #4 $84.40   5.139%   $88.7373   $88.74   $88.75   $88.70  
  Purchase #5 $164.31   9.175%   $179.3854   $179.39   $179.40   $179.40  
  Purchase #6 $63.76   6.749%   $68.0632   $68.06   $68.05   $68.10  
  Purchase #7 $101.46   3.694%   $105.2079   $105.21   $105.20   $105.20  
  7 purchase totals = $703.05       $756.4789   $756.48   $756.50   $756.50