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 $182.99   11.275%   $203.6221   $203.62   $203.60   $203.60  
  Purchase #2 $224.93   10.545%   $248.6489   $248.65   $248.65   $248.60  
  Purchase #3 $81.40   5.790%   $86.1131   $86.11   $86.10   $86.10  
  Purchase #4 $91.67   4.464%   $95.7621   $95.76   $95.75   $95.80  
  Purchase #5 $70.84   4.633%   $74.122   $74.12   $74.10   $74.10  
  Purchase #6 $39.46   8.783%   $42.9258   $42.93   $42.95   $42.90  
  Purchase #7 $238.37   10.828%   $264.1807   $264.18   $264.20   $264.20  
  7 purchase totals = $929.66       $1,015.3747   $1,015.37   $1,015.35   $1,015.30