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 $52.71   9.274%   $57.5983   $57.60   $57.60   $57.60  
  Purchase #2 $211.61   9.451%   $231.6093   $231.61   $231.60   $231.60  
  Purchase #3 $206.37   12.278%   $231.7081   $231.71   $231.70   $231.70  
  Purchase #4 $198.77   12.720%   $224.0535   $224.05   $224.05   $224.10  
  Purchase #5 $245.39   12.264%   $275.4846   $275.48   $275.50   $275.50  
  Purchase #6 $68.37   8.736%   $74.3428   $74.34   $74.35   $74.30  
  Purchase #7 $67.48   10.700%   $74.7004   $74.70   $74.70   $74.70  
  7 purchase totals = $1,050.70       $1,169.4970   $1,169.49   $1,169.50   $1,169.50