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 $208.96   11.626%   $233.2537   $233.25   $233.25   $233.30  
  Purchase #2 $168.41   4.360%   $175.7527   $175.75   $175.75   $175.80  
  Purchase #3 $228.74   8.161%   $247.4075   $247.41   $247.40   $247.40  
  Purchase #4 $12.86   10.301%   $14.1847   $14.18   $14.20   $14.20  
  Purchase #5 $217.29   4.260%   $226.5466   $226.55   $226.55   $226.50  
  Purchase #6 $91.90   13.641%   $104.4361   $104.44   $104.45   $104.40  
  Purchase #7 $20.84   10.315%   $22.9896   $22.99   $23.00   $23.00  
  7 purchase totals = $949.00       $1,024.5709   $1,024.57   $1,024.60   $1,024.60