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 $246.45   11.817%   $275.573   $275.57   $275.55   $275.60  
  Purchase #2 $141.35   5.594%   $149.2571   $149.26   $149.25   $149.30  
  Purchase #3 $237.39   6.814%   $253.5658   $253.57   $253.55   $253.60  
  Purchase #4 $157.38   5.278%   $165.6865   $165.69   $165.70   $165.70  
  Purchase #5 $211.27   7.356%   $226.811   $226.81   $226.80   $226.80  
  Purchase #6 $66.32   4.750%   $69.4702   $69.47   $69.45   $69.50  
  Purchase #7 $177.92   3.554%   $184.2433   $184.24   $184.25   $184.20  
  7 purchase totals = $1,238.08       $1,324.6069   $1,324.61   $1,324.55   $1,324.70