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 $235.98   11.422%   $262.9336   $262.93   $262.95   $262.90  
  Purchase #2 $204.46   12.311%   $229.6311   $229.63   $229.65   $229.60  
  Purchase #3 $113.57   4.569%   $118.759   $118.76   $118.75   $118.80  
  Purchase #4 $81.96   8.680%   $89.0741   $89.07   $89.05   $89.10  
  Purchase #5 $88.45   12.652%   $99.6407   $99.64   $99.65   $99.60  
  Purchase #6 $170.79   5.527%   $180.2296   $180.23   $180.25   $180.20  
  Purchase #7 $139.60   6.665%   $148.9043   $148.90   $148.90   $148.90  
  7 purchase totals = $1,034.81       $1,129.1724   $1,129.16   $1,129.20   $1,129.10