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 $211.48   10.611%   $233.9201   $233.92   $233.90   $233.90  
  Purchase #2 $224.58   4.798%   $235.3553   $235.36   $235.35   $235.40  
  Purchase #3 $228.90   4.645%   $239.5324   $239.53   $239.55   $239.50  
  Purchase #4 $96.47   12.865%   $108.8809   $108.88   $108.90   $108.90  
  Purchase #5 $127.70   8.563%   $138.635   $138.64   $138.65   $138.60  
  Purchase #6 $204.42   8.298%   $221.3828   $221.38   $221.40   $221.40  
  Purchase #7 $51.58   12.630%   $58.0946   $58.09   $58.10   $58.10  
  7 purchase totals = $1,145.13       $1,235.8011   $1,235.80   $1,235.85   $1,235.80