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 $184.59   9.135%   $201.4523   $201.45   $201.45   $201.50  
  Purchase #2 $80.63   9.624%   $88.3898   $88.39   $88.40   $88.40  
  Purchase #3 $24.97   3.442%   $25.8295   $25.83   $25.85   $25.80  
  Purchase #4 $131.49   3.578%   $136.1947   $136.19   $136.20   $136.20  
  Purchase #5 $109.62   12.734%   $123.579   $123.58   $123.60   $123.60  
  Purchase #6 $234.61   8.356%   $254.214   $254.21   $254.20   $254.20  
  Purchase #7 $233.68   9.482%   $255.8375   $255.84   $255.85   $255.80  
  7 purchase totals = $999.59       $1,085.4968   $1,085.49   $1,085.55   $1,085.50