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 $164.32   5.799%   $173.8489   $173.85   $173.85   $173.80  
  Purchase #2 $165.30   3.656%   $171.3434   $171.34   $171.35   $171.30  
  Purchase #3 $24.38   6.575%   $25.983   $25.98   $26.00   $26.00  
  Purchase #4 $231.81   13.370%   $262.803   $262.80   $262.80   $262.80  
  Purchase #5 $69.40   9.252%   $75.8209   $75.82   $75.80   $75.80  
  Purchase #6 $21.48   5.395%   $22.6388   $22.64   $22.65   $22.60  
  Purchase #7 $45.79   9.191%   $49.9986   $50.00   $50.00   $50.00  
  7 purchase totals = $722.48       $782.4366   $782.43   $782.45   $782.30