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 $207.58   9.206%   $226.6898   $226.69   $226.70   $226.70  
  Purchase #2 $61.34   5.350%   $64.6217   $64.62   $64.60   $64.60  
  Purchase #3 $137.68   5.648%   $145.4562   $145.46   $145.45   $145.50  
  Purchase #4 $200.50   13.799%   $228.167   $228.17   $228.15   $228.20  
  Purchase #5 $90.69   6.271%   $96.3772   $96.38   $96.40   $96.40  
  Purchase #6 $114.66   12.803%   $129.3399   $129.34   $129.35   $129.30  
  Purchase #7 $211.79   9.784%   $232.5115   $232.51   $232.50   $232.50  
  7 purchase totals = $1,024.24       $1,123.1633   $1,123.17   $1,123.15   $1,123.20