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 $132.95   10.305%   $146.6505   $146.65   $146.65   $146.70  
  Purchase #2 $90.62   3.514%   $93.8044   $93.80   $93.80   $93.80  
  Purchase #3 $58.31   11.365%   $64.9369   $64.94   $64.95   $64.90  
  Purchase #4 $219.82   4.359%   $229.402   $229.40   $229.40   $229.40  
  Purchase #5 $127.66   11.253%   $142.0256   $142.03   $142.05   $142.00  
  Purchase #6 $243.32   10.250%   $268.2603   $268.26   $268.25   $268.30  
  Purchase #7 $111.58   5.214%   $117.3978   $117.40   $117.40   $117.40  
  7 purchase totals = $984.26       $1,062.4775   $1,062.48   $1,062.50   $1,062.50