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 $239.51   8.211%   $259.1762   $259.18   $259.20   $259.20  
  Purchase #2 $125.84   12.123%   $141.0956   $141.10   $141.10   $141.10  
  Purchase #3 $234.96   9.295%   $256.7995   $256.80   $256.80   $256.80  
  Purchase #4 $60.78   4.787%   $63.6895   $63.69   $63.70   $63.70  
  Purchase #5 $43.62   5.676%   $46.0959   $46.10   $46.10   $46.10  
  Purchase #6 $132.58   3.269%   $136.914   $136.91   $136.90   $136.90  
  Purchase #7 $176.74   8.439%   $191.6551   $191.66   $191.65   $191.70  
  7 purchase totals = $1,014.03       $1,095.4258   $1,095.44   $1,095.45   $1,095.50