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 $152.46   13.798%   $173.4964   $173.50   $173.50   $173.50  
  Purchase #2 $148.62   3.183%   $153.3506   $153.35   $153.35   $153.40  
  Purchase #3 $129.30   12.456%   $145.4056   $145.41   $145.40   $145.40  
  Purchase #4 $53.42   5.491%   $56.3533   $56.35   $56.35   $56.40  
  Purchase #5 $73.36   5.415%   $77.3324   $77.33   $77.35   $77.30  
  Purchase #6 $91.41   11.627%   $102.0382   $102.04   $102.05   $102.00  
  Purchase #7 $26.35   12.130%   $29.5463   $29.55   $29.55   $29.50  
  7 purchase totals = $674.92       $737.5228   $737.53   $737.55   $737.50