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 $55.62   5.509%   $58.6841   $58.68   $58.70   $58.70  
  Purchase #2 $23.46   5.408%   $24.7287   $24.73   $24.75   $24.70  
  Purchase #3 $250.77   13.813%   $285.4089   $285.41   $285.40   $285.40  
  Purchase #4 $87.28   9.554%   $95.6187   $95.62   $95.60   $95.60  
  Purchase #5 $124.72   11.125%   $138.5951   $138.60   $138.60   $138.60  
  Purchase #6 $182.73   8.355%   $197.9971   $198.00   $198.00   $198.00  
  Purchase #7 $27.98   11.548%   $31.2111   $31.21   $31.20   $31.20  
  7 purchase totals = $752.56       $832.2437   $832.25   $832.25   $832.20