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 $241.59   9.383%   $264.2584   $264.26   $264.25   $264.30  
  Purchase #2 $217.76   3.269%   $224.8786   $224.88   $224.90   $224.90  
  Purchase #3 $43.85   11.553%   $48.916   $48.92   $48.90   $48.90  
  Purchase #4 $14.90   5.516%   $15.7219   $15.72   $15.70   $15.70  
  Purchase #5 $204.38   3.624%   $211.7867   $211.79   $211.80   $211.80  
  Purchase #6 $13.54   13.425%   $15.3577   $15.36   $15.35   $15.40  
  Purchase #7 $227.33   11.834%   $254.2322   $254.23   $254.25   $254.20  
  7 purchase totals = $963.35       $1,035.1515   $1,035.16   $1,035.15   $1,035.20