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 $242.39   8.764%   $263.6331   $263.63   $263.65   $263.60  
  Purchase #2 $56.36   13.786%   $64.1298   $64.13   $64.15   $64.10  
  Purchase #3 $12.63   6.462%   $13.4462   $13.45   $13.45   $13.40  
  Purchase #4 $44.92   10.156%   $49.4821   $49.48   $49.50   $49.50  
  Purchase #5 $237.66   3.518%   $246.0209   $246.02   $246.00   $246.00  
  Purchase #6 $73.52   12.330%   $82.585   $82.59   $82.60   $82.60  
  Purchase #7 $76.26   8.820%   $82.9861   $82.99   $83.00   $83.00  
  7 purchase totals = $743.74       $802.2832   $802.29   $802.35   $802.20