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 $56.61   5.225%   $59.5679   $59.57   $59.55   $59.60  
  Purchase #2 $131.64   8.319%   $142.5911   $142.59   $142.60   $142.60  
  Purchase #3 $230.37   7.629%   $247.9449   $247.94   $247.95   $247.90  
  Purchase #4 $221.91   10.423%   $245.0397   $245.04   $245.05   $245.00  
  Purchase #5 $214.93   12.118%   $240.9752   $240.98   $241.00   $241.00  
  Purchase #6 $97.76   7.213%   $104.8114   $104.81   $104.80   $104.80  
  Purchase #7 $88.57   6.657%   $94.4661   $94.47   $94.45   $94.50  
  7 purchase totals = $1,041.79       $1,135.3963   $1,135.40   $1,135.40   $1,135.40