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 $96.37   10.153%   $106.1544   $106.15   $106.15   $106.20  
  Purchase #2 $39.42   5.198%   $41.4691   $41.47   $41.45   $41.50  
  Purchase #3 $24.99   4.142%   $26.0251   $26.03   $26.05   $26.00  
  Purchase #4 $232.29   5.147%   $244.246   $244.25   $244.25   $244.20  
  Purchase #5 $241.63   6.266%   $256.7705   $256.77   $256.75   $256.80  
  Purchase #6 $61.80   11.585%   $68.9595   $68.96   $68.95   $69.00  
  Purchase #7 $100.83   13.589%   $114.5318   $114.53   $114.55   $114.50  
  7 purchase totals = $797.33       $858.1564   $858.16   $858.15   $858.20