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 $93.40   9.821%   $102.5728   $102.57   $102.55   $102.60  
  Purchase #2 $240.66   5.190%   $253.1503   $253.15   $253.15   $253.20  
  Purchase #3 $223.25   13.666%   $253.7593   $253.76   $253.75   $253.80  
  Purchase #4 $177.73   5.663%   $187.7948   $187.79   $187.80   $187.80  
  Purchase #5 $40.99   11.841%   $45.8436   $45.84   $45.85   $45.80  
  Purchase #6 $215.71   8.271%   $233.5514   $233.55   $233.55   $233.60  
  Purchase #7 $119.28   6.124%   $126.5847   $126.58   $126.60   $126.60  
  7 purchase totals = $1,111.02       $1,203.2569   $1,203.24   $1,203.25   $1,203.40