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 $59.74   8.759%   $64.9726   $64.97   $64.95   $65.00  
  Purchase #2 $114.46   4.485%   $119.5935   $119.59   $119.60   $119.60  
  Purchase #3 $220.72   3.132%   $227.633   $227.63   $227.65   $227.60  
  Purchase #4 $137.50   13.196%   $155.6445   $155.64   $155.65   $155.60  
  Purchase #5 $184.84   3.258%   $190.8621   $190.86   $190.85   $190.90  
  Purchase #6 $134.90   10.104%   $148.5303   $148.53   $148.55   $148.50  
  Purchase #7 $98.60   9.356%   $107.825   $107.83   $107.85   $107.80  
  7 purchase totals = $950.76       $1,015.0610   $1,015.05   $1,015.10   $1,015.00