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 $136.95   8.494%   $148.5825   $148.58   $148.60   $148.60  
  Purchase #2 $158.82   5.576%   $167.6758   $167.68   $167.70   $167.70  
  Purchase #3 $108.42   12.691%   $122.1796   $122.18   $122.20   $122.20  
  Purchase #4 $233.81   3.187%   $241.2615   $241.26   $241.25   $241.30  
  Purchase #5 $100.81   5.805%   $106.662   $106.66   $106.65   $106.70  
  Purchase #6 $142.75   6.251%   $151.6733   $151.67   $151.65   $151.70  
  Purchase #7 $68.84   13.328%   $78.015   $78.02   $78.00   $78.00  
  7 purchase totals = $950.40       $1,016.0497   $1,016.05   $1,016.05   $1,016.20