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 $174.39   4.654%   $182.5061   $182.51   $182.50   $182.50  
  Purchase #2 $108.80   10.149%   $119.8421   $119.84   $119.85   $119.80  
  Purchase #3 $147.72   5.597%   $155.9879   $155.99   $156.00   $156.00  
  Purchase #4 $171.64   8.800%   $186.7443   $186.74   $186.75   $186.70  
  Purchase #5 $101.27   8.533%   $109.9114   $109.91   $109.90   $109.90  
  Purchase #6 $53.30   5.111%   $56.0242   $56.02   $56.00   $56.00  
  Purchase #7 $193.37   11.565%   $215.7332   $215.73   $215.75   $215.70  
  7 purchase totals = $950.49       $1,026.7492   $1,026.74   $1,026.75   $1,026.60