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 $87.88   8.788%   $95.6029   $95.60   $95.60   $95.60  
  Purchase #2 $26.72   8.676%   $29.0382   $29.04   $29.05   $29.00  
  Purchase #3 $166.36   4.543%   $173.9177   $173.92   $173.90   $173.90  
  Purchase #4 $150.66   6.569%   $160.5569   $160.56   $160.55   $160.60  
  Purchase #5 $165.25   9.757%   $181.3734   $181.37   $181.35   $181.40  
  Purchase #6 $245.69   3.607%   $254.552   $254.55   $254.55   $254.60  
  Purchase #7 $42.86   11.592%   $47.8283   $47.83   $47.85   $47.80  
  7 purchase totals = $885.42       $942.8694   $942.87   $942.85   $942.90