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 $58.92   13.783%   $67.0409   $67.04   $67.05   $67.00  
  Purchase #2 $221.73   7.115%   $237.5061   $237.51   $237.50   $237.50  
  Purchase #3 $53.44   7.854%   $57.6372   $57.64   $57.65   $57.60  
  Purchase #4 $5.84   3.609%   $6.0508   $6.05   $6.05   $6.10  
  Purchase #5 $232.94   4.724%   $243.9441   $243.94   $243.95   $243.90  
  Purchase #6 $202.61   4.127%   $210.9717   $210.97   $210.95   $211.00  
  Purchase #7 $235.94   5.361%   $248.5887   $248.59   $248.60   $248.60  
  7 purchase totals = $1,011.42       $1,071.7395   $1,071.74   $1,071.75   $1,071.70