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 $175.97   9.571%   $192.8121   $192.81   $192.80   $192.80  
  Purchase #2 $71.46   7.294%   $76.6723   $76.67   $76.65   $76.70  
  Purchase #3 $91.64   10.425%   $101.1935   $101.19   $101.20   $101.20  
  Purchase #4 $205.79   5.580%   $217.2731   $217.27   $217.25   $217.30  
  Purchase #5 $190.34   11.372%   $211.9855   $211.99   $212.00   $212.00  
  Purchase #6 $176.77   3.746%   $183.3918   $183.39   $183.40   $183.40  
  Purchase #7 $48.55   6.627%   $51.7674   $51.77   $51.75   $51.80  
  7 purchase totals = $960.52       $1,035.0957   $1,035.09   $1,035.05   $1,035.20