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 $61.42   10.789%   $68.0466   $68.05   $68.05   $68.00  
  Purchase #2 $242.50   7.813%   $261.4465   $261.45   $261.45   $261.40  
  Purchase #3 $221.81   9.606%   $243.1171   $243.12   $243.10   $243.10  
  Purchase #4 $25.93   5.224%   $27.2846   $27.28   $27.30   $27.30  
  Purchase #5 $209.89   3.738%   $217.7357   $217.74   $217.75   $217.70  
  Purchase #6 $12.85   13.333%   $14.5633   $14.56   $14.55   $14.60  
  Purchase #7 $185.87   6.398%   $197.762   $197.76   $197.75   $197.80  
  7 purchase totals = $960.27       $1,029.9558   $1,029.96   $1,029.95   $1,029.90