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 $197.38   11.350%   $219.7826   $219.78   $219.80   $219.80  
  Purchase #2 $151.99   7.330%   $163.1309   $163.13   $163.15   $163.10  
  Purchase #3 $158.25   4.554%   $165.4567   $165.46   $165.45   $165.50  
  Purchase #4 $120.78   10.367%   $133.3013   $133.30   $133.30   $133.30  
  Purchase #5 $17.88   11.507%   $19.9375   $19.94   $19.95   $19.90  
  Purchase #6 $37.33   5.489%   $39.379   $39.38   $39.40   $39.40  
  Purchase #7 $224.89   10.516%   $248.5394   $248.54   $248.55   $248.50  
  7 purchase totals = $908.50       $989.5274   $989.53   $989.60   $989.50