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 $183.53   7.306%   $196.9387   $196.94   $196.95   $196.90  
  Purchase #2 $20.96   11.315%   $23.3316   $23.33   $23.35   $23.30  
  Purchase #3 $126.94   4.373%   $132.4911   $132.49   $132.50   $132.50  
  Purchase #4 $95.55   7.281%   $102.507   $102.51   $102.50   $102.50  
  Purchase #5 $152.66   6.826%   $163.0806   $163.08   $163.10   $163.10  
  Purchase #6 $192.66   10.754%   $213.3787   $213.38   $213.40   $213.40  
  Purchase #7 $176.48   9.420%   $193.1044   $193.10   $193.10   $193.10  
  7 purchase totals = $948.78       $1,024.8321   $1,024.83   $1,024.90   $1,024.80