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 $182.25   13.354%   $206.5877   $206.59   $206.60   $206.60  
  Purchase #2 $68.63   8.868%   $74.7161   $74.72   $74.70   $74.70  
  Purchase #3 $110.55   11.692%   $123.4755   $123.48   $123.50   $123.50  
  Purchase #4 $159.56   12.426%   $179.3869   $179.39   $179.40   $179.40  
  Purchase #5 $155.29   9.844%   $170.5767   $170.58   $170.60   $170.60  
  Purchase #6 $217.77   4.648%   $227.8919   $227.89   $227.90   $227.90  
  Purchase #7 $29.95   6.872%   $32.0082   $32.01   $32.00   $32.00  
  7 purchase totals = $924.00       $1,014.6430   $1,014.66   $1,014.70   $1,014.70