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 $47.87   8.873%   $52.1175   $52.12   $52.10   $52.10  
  Purchase #2 $38.94   11.291%   $43.3367   $43.34   $43.35   $43.30  
  Purchase #3 $181.80   8.832%   $197.8566   $197.86   $197.85   $197.90  
  Purchase #4 $236.27   4.840%   $247.7055   $247.71   $247.70   $247.70  
  Purchase #5 $75.75   12.635%   $85.321   $85.32   $85.30   $85.30  
  Purchase #6 $169.69   8.225%   $183.647   $183.65   $183.65   $183.60  
  Purchase #7 $78.46   12.266%   $88.0839   $88.08   $88.10   $88.10  
  7 purchase totals = $828.78       $898.0682   $898.08   $898.05   $898.00