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 $145.76   7.259%   $156.3407   $156.34   $156.35   $156.30  
  Purchase #2 $230.37   4.803%   $241.4347   $241.43   $241.45   $241.40  
  Purchase #3 $29.68   12.440%   $33.3722   $33.37   $33.35   $33.40  
  Purchase #4 $213.76   8.126%   $231.1301   $231.13   $231.15   $231.10  
  Purchase #5 $33.44   3.696%   $34.6759   $34.68   $34.70   $34.70  
  Purchase #6 $194.90   13.777%   $221.7514   $221.75   $221.75   $221.80  
  Purchase #7 $247.65   13.716%   $281.6177   $281.62   $281.60   $281.60  
  7 purchase totals = $1,095.56       $1,200.3227   $1,200.32   $1,200.35   $1,200.30