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 $17.63   11.131%   $19.5924   $19.59   $19.60   $19.60  
  Purchase #2 $228.56   8.614%   $248.2482   $248.25   $248.25   $248.20  
  Purchase #3 $71.82   6.188%   $76.2642   $76.26   $76.25   $76.30  
  Purchase #4 $168.72   6.265%   $179.2903   $179.29   $179.30   $179.30  
  Purchase #5 $247.92   6.348%   $263.658   $263.66   $263.65   $263.70  
  Purchase #6 $207.44   7.575%   $223.1536   $223.15   $223.15   $223.20  
  Purchase #7 $75.67   3.125%   $78.0347   $78.03   $78.05   $78.00  
  7 purchase totals = $1,017.76       $1,088.2414   $1,088.23   $1,088.25   $1,088.30