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 $193.49   7.278%   $207.5722   $207.57   $207.55   $207.60  
  Purchase #2 $53.97   8.398%   $58.5024   $58.50   $58.50   $58.50  
  Purchase #3 $231.69   8.669%   $251.7752   $251.78   $251.80   $251.80  
  Purchase #4 $235.43   6.599%   $250.966   $250.97   $250.95   $251.00  
  Purchase #5 $192.99   12.823%   $217.7371   $217.74   $217.75   $217.70  
  Purchase #6 $167.93   6.318%   $178.5398   $178.54   $178.55   $178.50  
  Purchase #7 $180.97   11.334%   $201.4811   $201.48   $201.50   $201.50  
  7 purchase totals = $1,256.47       $1,366.5738   $1,366.58   $1,366.60   $1,366.60