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 $202.35   10.697%   $223.9954   $224.00   $224.00   $224.00  
  Purchase #2 $78.83   12.834%   $88.947   $88.95   $88.95   $88.90  
  Purchase #3 $236.52   5.261%   $248.9633   $248.96   $248.95   $249.00  
  Purchase #4 $114.61   6.697%   $122.2854   $122.29   $122.30   $122.30  
  Purchase #5 $64.70   7.609%   $69.623   $69.62   $69.60   $69.60  
  Purchase #6 $121.56   10.734%   $134.6083   $134.61   $134.60   $134.60  
  Purchase #7 $135.81   8.547%   $147.4177   $147.42   $147.40   $147.40  
  7 purchase totals = $954.38       $1,035.8401   $1,035.85   $1,035.80   $1,035.80