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 $201.76   5.673%   $213.2058   $213.21   $213.20   $213.20  
  Purchase #2 $118.36   10.605%   $130.9121   $130.91   $130.90   $130.90  
  Purchase #3 $184.30   7.786%   $198.6496   $198.65   $198.65   $198.60  
  Purchase #4 $221.26   10.764%   $245.0764   $245.08   $245.10   $245.10  
  Purchase #5 $87.61   4.614%   $91.6523   $91.65   $91.65   $91.70  
  Purchase #6 $26.55   11.542%   $29.6144   $29.61   $29.60   $29.60  
  Purchase #7 $141.41   3.252%   $146.0087   $146.01   $146.00   $146.00  
  7 purchase totals = $981.25       $1,055.1193   $1,055.12   $1,055.10   $1,055.10