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 $165.83   10.661%   $183.5091   $183.51   $183.50   $183.50  
  Purchase #2 $5.79   4.614%   $6.0572   $6.06   $6.05   $6.10  
  Purchase #3 $127.34   6.672%   $135.8361   $135.84   $135.85   $135.80  
  Purchase #4 $193.89   12.371%   $217.8761   $217.88   $217.90   $217.90  
  Purchase #5 $134.67   12.621%   $151.6667   $151.67   $151.65   $151.70  
  Purchase #6 $82.91   11.709%   $92.6179   $92.62   $92.60   $92.60  
  Purchase #7 $157.83   7.847%   $170.2149   $170.21   $170.20   $170.20  
  7 purchase totals = $868.26       $957.7780   $957.79   $957.75   $957.80