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 $250.85   10.144%   $276.2962   $276.30   $276.30   $276.30  
  Purchase #2 $18.85   8.118%   $20.3802   $20.38   $20.40   $20.40  
  Purchase #3 $231.94   3.227%   $239.4247   $239.42   $239.40   $239.40  
  Purchase #4 $165.91   13.768%   $188.7525   $188.75   $188.75   $188.80  
  Purchase #5 $43.78   8.331%   $47.4273   $47.43   $47.45   $47.40  
  Purchase #6 $88.28   6.226%   $93.7763   $93.78   $93.80   $93.80  
  Purchase #7 $151.58   7.534%   $163   $163.00   $163.00   $163.00  
  7 purchase totals = $951.19       $1,029.0572   $1,029.06   $1,029.10   $1,029.10