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 $241.29   11.697%   $269.5137   $269.51   $269.50   $269.50  
  Purchase #2 $224.76   9.817%   $246.8247   $246.82   $246.80   $246.80  
  Purchase #3 $7.85   10.799%   $8.6977   $8.70   $8.70   $8.70  
  Purchase #4 $145.95   11.664%   $162.9736   $162.97   $162.95   $163.00  
  Purchase #5 $119.63   8.566%   $129.8775   $129.88   $129.90   $129.90  
  Purchase #6 $179.57   10.776%   $198.9205   $198.92   $198.90   $198.90  
  Purchase #7 $41.33   4.738%   $43.2882   $43.29   $43.30   $43.30  
  7 purchase totals = $960.38       $1,060.0959   $1,060.09   $1,060.05   $1,060.10