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 $148.28   3.302%   $153.1762   $153.18   $153.20   $153.20  
  Purchase #2 $53.96   3.356%   $55.7709   $55.77   $55.75   $55.80  
  Purchase #3 $122.28   8.639%   $132.8438   $132.84   $132.85   $132.80  
  Purchase #4 $55.81   7.496%   $59.9935   $59.99   $60.00   $60.00  
  Purchase #5 $111.32   7.793%   $119.9952   $120.00   $120.00   $120.00  
  Purchase #6 $50.43   11.722%   $56.3414   $56.34   $56.35   $56.30  
  Purchase #7 $143.84   5.512%   $151.7685   $151.77   $151.75   $151.80  
  7 purchase totals = $685.92       $729.8895   $729.89   $729.90   $729.90