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 $241.38   8.272%   $261.347   $261.35   $261.35   $261.30  
  Purchase #2 $56.47   9.318%   $61.7319   $61.73   $61.75   $61.70  
  Purchase #3 $181.83   10.620%   $201.1403   $201.14   $201.15   $201.10  
  Purchase #4 $17.67   9.113%   $19.2803   $19.28   $19.30   $19.30  
  Purchase #5 $238.62   13.553%   $270.9602   $270.96   $270.95   $271.00  
  Purchase #6 $221.64   12.319%   $248.9438   $248.94   $248.95   $248.90  
  Purchase #7 $107.65   9.266%   $117.6248   $117.62   $117.60   $117.60  
  7 purchase totals = $1,065.26       $1,181.0283   $1,181.02   $1,181.05   $1,180.90