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 $113.84   9.592%   $124.7595   $124.76   $124.75   $124.80  
  Purchase #2 $61.43   4.723%   $64.3313   $64.33   $64.35   $64.30  
  Purchase #3 $15.87   10.796%   $17.5833   $17.58   $17.60   $17.60  
  Purchase #4 $64.34   3.825%   $66.801   $66.80   $66.80   $66.80  
  Purchase #5 $165.48   9.368%   $180.9822   $180.98   $181.00   $181.00  
  Purchase #6 $23.25   7.564%   $25.0086   $25.01   $25.00   $25.00  
  Purchase #7 $146.60   7.481%   $157.5671   $157.57   $157.55   $157.60  
  7 purchase totals = $590.81       $637.0330   $637.03   $637.05   $637.10