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 $207.88   12.158%   $233.1541   $233.15   $233.15   $233.20  
  Purchase #2 $56.30   9.596%   $61.7025   $61.70   $61.70   $61.70  
  Purchase #3 $210.49   6.571%   $224.3213   $224.32   $224.30   $224.30  
  Purchase #4 $36.73   4.107%   $38.2385   $38.24   $38.25   $38.20  
  Purchase #5 $228.71   8.196%   $247.4551   $247.46   $247.45   $247.50  
  Purchase #6 $243.90   9.258%   $266.4803   $266.48   $266.50   $266.50  
  Purchase #7 $229.64   10.566%   $253.9038   $253.90   $253.90   $253.90  
  7 purchase totals = $1,213.65       $1,325.2556   $1,325.25   $1,325.25   $1,325.30