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 $212.60   12.593%   $239.3727   $239.37   $239.35   $239.40  
  Purchase #2 $142.87   3.337%   $147.6376   $147.64   $147.65   $147.60  
  Purchase #3 $104.85   11.258%   $116.654   $116.65   $116.65   $116.70  
  Purchase #4 $177.91   12.396%   $199.9637   $199.96   $199.95   $200.00  
  Purchase #5 $44.95   3.279%   $46.4239   $46.42   $46.40   $46.40  
  Purchase #6 $78.66   9.814%   $86.3797   $86.38   $86.40   $86.40  
  Purchase #7 $233.33   5.133%   $245.3068   $245.31   $245.30   $245.30  
  7 purchase totals = $995.17       $1,081.7384   $1,081.73   $1,081.70   $1,081.80