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 $73.92   8.152%   $79.946   $79.95   $79.95   $79.90  
  Purchase #2 $70.63   5.211%   $74.3105   $74.31   $74.30   $74.30  
  Purchase #3 $248.33   9.428%   $271.7426   $271.74   $271.75   $271.70  
  Purchase #4 $211.30   10.367%   $233.2055   $233.21   $233.20   $233.20  
  Purchase #5 $54.74   12.381%   $61.5174   $61.52   $61.50   $61.50  
  Purchase #6 $248.34   13.681%   $282.3154   $282.32   $282.30   $282.30  
  Purchase #7 $19.33   4.540%   $20.2076   $20.21   $20.20   $20.20  
  7 purchase totals = $926.59       $1,023.2450   $1,023.26   $1,023.20   $1,023.10