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 $154.99   7.397%   $166.4546   $166.45   $166.45   $166.50  
  Purchase #2 $215.60   6.546%   $229.7132   $229.71   $229.70   $229.70  
  Purchase #3 $133.37   5.379%   $140.544   $140.54   $140.55   $140.50  
  Purchase #4 $227.64   12.670%   $256.482   $256.48   $256.50   $256.50  
  Purchase #5 $146.96   4.360%   $153.3675   $153.37   $153.35   $153.40  
  Purchase #6 $203.98   7.808%   $219.9068   $219.91   $219.90   $219.90  
  Purchase #7 $39.55   11.847%   $44.2355   $44.24   $44.25   $44.20  
  7 purchase totals = $1,122.09       $1,210.7036   $1,210.70   $1,210.70   $1,210.70