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 $242.45   8.816%   $263.8244   $263.82   $263.80   $263.80  
  Purchase #2 $119.57   12.327%   $134.3094   $134.31   $134.30   $134.30  
  Purchase #3 $76.32   12.105%   $85.5585   $85.56   $85.55   $85.60  
  Purchase #4 $246.88   13.350%   $279.8385   $279.84   $279.85   $279.80  
  Purchase #5 $124.63   5.625%   $131.6404   $131.64   $131.65   $131.60  
  Purchase #6 $155.67   13.552%   $176.7664   $176.77   $176.75   $176.80  
  Purchase #7 $198.30   12.578%   $223.2422   $223.24   $223.25   $223.20  
  7 purchase totals = $1,163.82       $1,295.1798   $1,295.18   $1,295.15   $1,295.10