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 $48.47   4.295%   $50.5518   $50.55   $50.55   $50.60  
  Purchase #2 $177.55   11.665%   $198.2612   $198.26   $198.25   $198.30  
  Purchase #3 $39.79   4.479%   $41.5722   $41.57   $41.55   $41.60  
  Purchase #4 $236.33   13.280%   $267.7146   $267.71   $267.70   $267.70  
  Purchase #5 $234.61   5.664%   $247.8983   $247.90   $247.90   $247.90  
  Purchase #6 $87.93   5.454%   $92.7257   $92.73   $92.75   $92.70  
  Purchase #7 $170.76   3.302%   $176.3985   $176.40   $176.40   $176.40  
  7 purchase totals = $995.44       $1,075.1223   $1,075.12   $1,075.10   $1,075.20