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 $166.50   6.364%   $177.0961   $177.10   $177.10   $177.10  
  Purchase #2 $51.34   13.547%   $58.295   $58.30   $58.30   $58.30  
  Purchase #3 $146.80   5.628%   $155.0619   $155.06   $155.05   $155.10  
  Purchase #4 $104.38   7.811%   $112.5331   $112.53   $112.55   $112.50  
  Purchase #5 $113.44   6.740%   $121.0859   $121.09   $121.10   $121.10  
  Purchase #6 $250.49   7.474%   $269.2116   $269.21   $269.20   $269.20  
  Purchase #7 $123.78   5.222%   $130.2438   $130.24   $130.25   $130.20  
  7 purchase totals = $956.73       $1,023.5274   $1,023.53   $1,023.55   $1,023.50