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 $81.53   12.276%   $91.5386   $91.54   $91.55   $91.50  
  Purchase #2 $211.81   7.239%   $227.1429   $227.14   $227.15   $227.10  
  Purchase #3 $193.94   11.855%   $216.9316   $216.93   $216.95   $216.90  
  Purchase #4 $211.66   9.533%   $231.8375   $231.84   $231.85   $231.80  
  Purchase #5 $48.28   13.820%   $54.9523   $54.95   $54.95   $55.00  
  Purchase #6 $162.89   5.574%   $171.9695   $171.97   $171.95   $172.00  
  Purchase #7 $62.81   10.214%   $69.2254   $69.23   $69.25   $69.20  
  7 purchase totals = $972.92       $1,063.5978   $1,063.60   $1,063.65   $1,063.50