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 $173.99   5.457%   $183.4846   $183.48   $183.50   $183.50  
  Purchase #2 $248.26   6.197%   $263.6447   $263.64   $263.65   $263.60  
  Purchase #3 $162.93   9.632%   $178.6234   $178.62   $178.60   $178.60  
  Purchase #4 $33.94   12.390%   $38.1452   $38.15   $38.15   $38.10  
  Purchase #5 $59.76   11.507%   $66.6366   $66.64   $66.65   $66.60  
  Purchase #6 $151.86   6.431%   $161.6261   $161.63   $161.65   $161.60  
  Purchase #7 $167.65   9.362%   $183.3454   $183.35   $183.35   $183.30  
  7 purchase totals = $998.39       $1,075.5060   $1,075.51   $1,075.55   $1,075.30