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 $66.34   4.220%   $69.1395   $69.14   $69.15   $69.10  
  Purchase #2 $233.64   13.518%   $265.2235   $265.22   $265.20   $265.20  
  Purchase #3 $165.46   7.230%   $177.4228   $177.42   $177.40   $177.40  
  Purchase #4 $131.93   7.828%   $142.2575   $142.26   $142.25   $142.30  
  Purchase #5 $118.85   9.231%   $129.821   $129.82   $129.80   $129.80  
  Purchase #6 $131.80   9.414%   $144.2077   $144.21   $144.20   $144.20  
  Purchase #7 $151.60   5.798%   $160.3898   $160.39   $160.40   $160.40  
  7 purchase totals = $999.62       $1,088.4618   $1,088.46   $1,088.40   $1,088.40