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 $26.56   4.463%   $27.7454   $27.75   $27.75   $27.70  
  Purchase #2 $61.92   7.141%   $66.3417   $66.34   $66.35   $66.30  
  Purchase #3 $232.76   10.628%   $257.4977   $257.50   $257.50   $257.50  
  Purchase #4 $82.87   6.227%   $88.0303   $88.03   $88.05   $88.00  
  Purchase #5 $39.49   9.777%   $43.3509   $43.35   $43.35   $43.40  
  Purchase #6 $222.27   11.437%   $247.691   $247.69   $247.70   $247.70  
  Purchase #7 $234.68   11.685%   $262.1024   $262.10   $262.10   $262.10  
  7 purchase totals = $900.55       $992.7594   $992.76   $992.80   $992.70