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 $57.70   11.159%   $64.1387   $64.14   $64.15   $64.10  
  Purchase #2 $227.34   3.601%   $235.5265   $235.53   $235.55   $235.50  
  Purchase #3 $123.78   6.609%   $131.9606   $131.96   $131.95   $132.00  
  Purchase #4 $227.48   7.551%   $244.657   $244.66   $244.65   $244.70  
  Purchase #5 $243.84   6.307%   $259.219   $259.22   $259.20   $259.20  
  Purchase #6 $130.78   6.716%   $139.5632   $139.56   $139.55   $139.60  
  Purchase #7 $117.92   7.439%   $126.6921   $126.69   $126.70   $126.70  
  7 purchase totals = $1,128.84       $1,201.7571   $1,201.76   $1,201.75   $1,201.80