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 $186.43   8.704%   $202.6569   $202.66   $202.65   $202.70  
  Purchase #2 $250.80   4.302%   $261.5894   $261.59   $261.60   $261.60  
  Purchase #3 $232.39   3.662%   $240.9001   $240.90   $240.90   $240.90  
  Purchase #4 $14.98   11.508%   $16.7039   $16.70   $16.70   $16.70  
  Purchase #5 $67.66   11.584%   $75.4977   $75.50   $75.50   $75.50  
  Purchase #6 $249.82   4.148%   $260.1825   $260.18   $260.20   $260.20  
  Purchase #7 $169.42   4.710%   $177.3997   $177.40   $177.40   $177.40  
  7 purchase totals = $1,171.50       $1,234.9302   $1,234.93   $1,234.95   $1,235.00