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 $98.49   7.150%   $105.532   $105.53   $105.55   $105.50  
  Purchase #2 $218.82   7.285%   $234.761   $234.76   $234.75   $234.80  
  Purchase #3 $207.29   4.371%   $216.3506   $216.35   $216.35   $216.40  
  Purchase #4 $236.68   13.554%   $268.7596   $268.76   $268.75   $268.80  
  Purchase #5 $235.86   3.285%   $243.608   $243.61   $243.60   $243.60  
  Purchase #6 $223.97   10.762%   $248.0737   $248.07   $248.05   $248.10  
  Purchase #7 $108.88   4.261%   $113.5194   $113.52   $113.50   $113.50  
  7 purchase totals = $1,329.99       $1,430.6043   $1,430.60   $1,430.55   $1,430.70