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 $200.39   13.581%   $227.605   $227.61   $227.60   $227.60  
  Purchase #2 $56.50   3.776%   $58.6334   $58.63   $58.65   $58.60  
  Purchase #3 $234.84   13.621%   $266.8276   $266.83   $266.85   $266.80  
  Purchase #4 $221.67   9.704%   $243.1809   $243.18   $243.20   $243.20  
  Purchase #5 $152.30   12.201%   $170.8821   $170.88   $170.90   $170.90  
  Purchase #6 $246.70   9.827%   $270.9432   $270.94   $270.95   $270.90  
  Purchase #7 $96.75   5.415%   $101.989   $101.99   $102.00   $102.00  
  7 purchase totals = $1,209.15       $1,340.0612   $1,340.06   $1,340.15   $1,340.00