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 $68.58   13.276%   $77.6847   $77.68   $77.70   $77.70  
  Purchase #2 $136.38   4.587%   $142.6358   $142.64   $142.65   $142.60  
  Purchase #3 $102.64   11.214%   $114.15   $114.15   $114.15   $114.20  
  Purchase #4 $163.30   6.284%   $173.5618   $173.56   $173.55   $173.60  
  Purchase #5 $168.26   10.536%   $185.9879   $185.99   $186.00   $186.00  
  Purchase #6 $35.64   5.147%   $37.4744   $37.47   $37.45   $37.50  
  Purchase #7 $200.77   4.769%   $210.3447   $210.34   $210.35   $210.30  
  7 purchase totals = $875.57       $941.8393   $941.83   $941.85   $941.90