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 $41.88   13.349%   $47.4706   $47.47   $47.45   $47.50  
  Purchase #2 $250.57   6.795%   $267.5962   $267.60   $267.60   $267.60  
  Purchase #3 $174.94   12.119%   $196.141   $196.14   $196.15   $196.10  
  Purchase #4 $50.67   12.173%   $56.8381   $56.84   $56.85   $56.80  
  Purchase #5 $213.90   6.787%   $228.4174   $228.42   $228.40   $228.40  
  Purchase #6 $203.26   3.581%   $210.5387   $210.54   $210.55   $210.50  
  Purchase #7 $207.74   9.670%   $227.8285   $227.83   $227.85   $227.80  
  7 purchase totals = $1,142.96       $1,234.8305   $1,234.84   $1,234.85   $1,234.70