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 $226.69   11.867%   $253.5913   $253.59   $253.60   $253.60  
  Purchase #2 $207.32   13.543%   $235.3973   $235.40   $235.40   $235.40  
  Purchase #3 $5.26   5.850%   $5.5677   $5.57   $5.55   $5.60  
  Purchase #4 $26.34   12.845%   $29.7234   $29.72   $29.70   $29.70  
  Purchase #5 $209.83   13.238%   $237.6073   $237.61   $237.60   $237.60  
  Purchase #6 $137.68   4.317%   $143.6236   $143.62   $143.60   $143.60  
  Purchase #7 $46.75   4.117%   $48.6747   $48.67   $48.65   $48.70  
  7 purchase totals = $859.87       $954.1853   $954.18   $954.10   $954.20