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 $87.93   12.108%   $98.5766   $98.58   $98.60   $98.60  
  Purchase #2 $106.60   11.177%   $118.5147   $118.51   $118.50   $118.50  
  Purchase #3 $132.45   4.454%   $138.3493   $138.35   $138.35   $138.30  
  Purchase #4 $145.78   10.810%   $161.5388   $161.54   $161.55   $161.50  
  Purchase #5 $240.70   12.264%   $270.2194   $270.22   $270.20   $270.20  
  Purchase #6 $141.74   11.398%   $157.8955   $157.90   $157.90   $157.90  
  Purchase #7 $211.25   13.187%   $239.1075   $239.11   $239.10   $239.10  
  7 purchase totals = $1,066.45       $1,184.2018   $1,184.21   $1,184.20   $1,184.10