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 $68.87   9.115%   $75.1475   $75.15   $75.15   $75.10  
  Purchase #2 $250.38   3.828%   $259.9645   $259.96   $259.95   $260.00  
  Purchase #3 $124.91   3.665%   $129.488   $129.49   $129.50   $129.50  
  Purchase #4 $173.41   4.873%   $181.8603   $181.86   $181.85   $181.90  
  Purchase #5 $184.70   4.668%   $193.3218   $193.32   $193.30   $193.30  
  Purchase #6 $21.99   11.546%   $24.529   $24.53   $24.55   $24.50  
  Purchase #7 $135.83   4.347%   $141.7345   $141.73   $141.75   $141.70  
  7 purchase totals = $960.09       $1,006.0456   $1,006.04   $1,006.05   $1,006.00