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 $179.35   8.461%   $194.5248   $194.52   $194.50   $194.50  
  Purchase #2 $210.40   11.170%   $233.9017   $233.90   $233.90   $233.90  
  Purchase #3 $243.61   11.340%   $271.2354   $271.24   $271.25   $271.20  
  Purchase #4 $67.90   11.453%   $75.6766   $75.68   $75.70   $75.70  
  Purchase #5 $20.73   8.636%   $22.5202   $22.52   $22.50   $22.50  
  Purchase #6 $247.63   8.777%   $269.3645   $269.36   $269.35   $269.40  
  Purchase #7 $218.32   7.369%   $234.408   $234.41   $234.40   $234.40  
  7 purchase totals = $1,187.94       $1,301.6312   $1,301.63   $1,301.60   $1,301.60