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 $138.42   10.272%   $152.6385   $152.64   $152.65   $152.60  
  Purchase #2 $82.63   4.157%   $86.0649   $86.06   $86.05   $86.10  
  Purchase #3 $95.60   8.188%   $103.4277   $103.43   $103.45   $103.40  
  Purchase #4 $242.39   3.835%   $251.6857   $251.69   $251.70   $251.70  
  Purchase #5 $63.83   7.856%   $68.8445   $68.84   $68.85   $68.80  
  Purchase #6 $73.29   4.401%   $76.5155   $76.52   $76.50   $76.50  
  Purchase #7 $234.52   12.235%   $263.2135   $263.21   $263.20   $263.20  
  7 purchase totals = $930.68       $1,002.3903   $1,002.39   $1,002.40   $1,002.30