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 $197.44   13.747%   $224.5821   $224.58   $224.60   $224.60  
  Purchase #2 $213.69   8.102%   $231.0032   $231.00   $231.00   $231.00  
  Purchase #3 $174.26   12.616%   $196.2446   $196.24   $196.25   $196.20  
  Purchase #4 $210.78   13.846%   $239.9646   $239.96   $239.95   $240.00  
  Purchase #5 $45.88   13.191%   $51.932   $51.93   $51.95   $51.90  
  Purchase #6 $191.64   5.845%   $202.8414   $202.84   $202.85   $202.80  
  Purchase #7 $147.75   8.404%   $160.1669   $160.17   $160.15   $160.20  
  7 purchase totals = $1,181.44       $1,306.7348   $1,306.72   $1,306.75   $1,306.70