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 $168.41   5.652%   $177.9285   $177.93   $177.95   $177.90  
  Purchase #2 $149.66   11.241%   $166.4833   $166.48   $166.50   $166.50  
  Purchase #3 $191.78   12.257%   $215.2865   $215.29   $215.30   $215.30  
  Purchase #4 $187.88   5.815%   $198.8052   $198.81   $198.80   $198.80  
  Purchase #5 $157.40   10.639%   $174.1458   $174.15   $174.15   $174.10  
  Purchase #6 $108.64   9.381%   $118.8315   $118.83   $118.85   $118.80  
  Purchase #7 $14.26   7.433%   $15.3199   $15.32   $15.30   $15.30  
  7 purchase totals = $978.03       $1,066.8007   $1,066.81   $1,066.85   $1,066.70