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 $116.60   3.586%   $120.7813   $120.78   $120.80   $120.80  
  Purchase #2 $42.40   6.613%   $45.2039   $45.20   $45.20   $45.20  
  Purchase #3 $6.39   4.221%   $6.6597   $6.66   $6.65   $6.70  
  Purchase #4 $114.27   12.386%   $128.4235   $128.42   $128.40   $128.40  
  Purchase #5 $141.70   4.256%   $147.7308   $147.73   $147.75   $147.70  
  Purchase #6 $83.45   3.506%   $86.3758   $86.38   $86.40   $86.40  
  Purchase #7 $12.27   11.505%   $13.6817   $13.68   $13.70   $13.70  
  7 purchase totals = $517.08       $548.8567   $548.85   $548.90   $548.90