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 $231.94   4.762%   $242.985   $242.99   $243.00   $243.00  
  Purchase #2 $102.85   13.457%   $116.6905   $116.69   $116.70   $116.70  
  Purchase #3 $54.54   12.205%   $61.1966   $61.20   $61.20   $61.20  
  Purchase #4 $52.75   6.742%   $56.3064   $56.31   $56.30   $56.30  
  Purchase #5 $179.99   9.103%   $196.3745   $196.37   $196.35   $196.40  
  Purchase #6 $182.57   11.724%   $203.9745   $203.97   $203.95   $204.00  
  Purchase #7 $199.61   7.552%   $214.6845   $214.68   $214.70   $214.70  
  7 purchase totals = $1,004.25       $1,092.2120   $1,092.21   $1,092.20   $1,092.30