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 $68.72   6.645%   $73.2864   $73.29   $73.30   $73.30  
  Purchase #2 $199.35   3.614%   $206.5545   $206.55   $206.55   $206.60  
  Purchase #3 $204.87   5.792%   $216.7361   $216.74   $216.75   $216.70  
  Purchase #4 $154.43   7.295%   $165.6957   $165.70   $165.70   $165.70  
  Purchase #5 $156.26   9.716%   $171.4422   $171.44   $171.45   $171.40  
  Purchase #6 $95.59   3.794%   $99.2167   $99.22   $99.20   $99.20  
  Purchase #7 $239.63   11.547%   $267.3001   $267.30   $267.30   $267.30  
  7 purchase totals = $1,118.85       $1,200.2317   $1,200.24   $1,200.25   $1,200.20