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 $5.91   3.692%   $6.1282   $6.13   $6.15   $6.10  
  Purchase #2 $195.99   8.179%   $212.02   $212.02   $212.00   $212.00  
  Purchase #3 $59.37   3.737%   $61.5887   $61.59   $61.60   $61.60  
  Purchase #4 $241.30   12.313%   $271.0113   $271.01   $271.00   $271.00  
  Purchase #5 $119.26   5.841%   $126.226   $126.23   $126.25   $126.20  
  Purchase #6 $118.90   7.252%   $127.5226   $127.52   $127.50   $127.50  
  Purchase #7 $121.83   13.483%   $138.2563   $138.26   $138.25   $138.30  
  7 purchase totals = $862.56       $942.7531   $942.76   $942.75   $942.70