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 $182.71   9.835%   $200.6795   $200.68   $200.70   $200.70  
  Purchase #2 $236.84   10.634%   $262.0256   $262.03   $262.05   $262.00  
  Purchase #3 $129.48   3.785%   $134.3808   $134.38   $134.40   $134.40  
  Purchase #4 $41.71   8.534%   $45.2695   $45.27   $45.25   $45.30  
  Purchase #5 $61.44   5.646%   $64.9089   $64.91   $64.90   $64.90  
  Purchase #6 $163.82   5.507%   $172.8416   $172.84   $172.85   $172.80  
  Purchase #7 $63.73   10.465%   $70.3993   $70.40   $70.40   $70.40  
  7 purchase totals = $879.73       $950.5052   $950.51   $950.55   $950.50