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 $84.88   12.814%   $95.7565   $95.76   $95.75   $95.80  
  Purchase #2 $14.67   13.429%   $16.64   $16.64   $16.65   $16.60  
  Purchase #3 $222.49   5.400%   $234.5045   $234.50   $234.50   $234.50  
  Purchase #4 $169.29   5.615%   $178.7956   $178.80   $178.80   $178.80  
  Purchase #5 $80.27   5.652%   $84.8069   $84.81   $84.80   $84.80  
  Purchase #6 $73.42   12.169%   $82.3545   $82.35   $82.35   $82.40  
  Purchase #7 $107.55   10.251%   $118.575   $118.58   $118.60   $118.60  
  7 purchase totals = $752.57       $811.4330   $811.44   $811.45   $811.50