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 $34.43   9.201%   $37.5979   $37.60   $37.60   $37.60  
  Purchase #2 $211.35   6.276%   $224.6143   $224.61   $224.60   $224.60  
  Purchase #3 $24.27   8.120%   $26.2407   $26.24   $26.25   $26.20  
  Purchase #4 $101.95   9.269%   $111.3997   $111.40   $111.40   $111.40  
  Purchase #5 $102.35   11.440%   $114.0588   $114.06   $114.05   $114.10  
  Purchase #6 $249.39   10.295%   $275.0647   $275.06   $275.05   $275.10  
  Purchase #7 $126.81   9.615%   $139.0028   $139.00   $139.00   $139.00  
  7 purchase totals = $850.55       $927.9789   $927.97   $927.95   $928.00