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 $154.96   11.702%   $173.0934   $173.09   $173.10   $173.10  
  Purchase #2 $202.90   10.579%   $224.3648   $224.36   $224.35   $224.40  
  Purchase #3 $34.38   11.623%   $38.376   $38.38   $38.40   $38.40  
  Purchase #4 $57.44   8.419%   $62.2759   $62.28   $62.30   $62.30  
  Purchase #5 $24.84   5.593%   $26.2293   $26.23   $26.25   $26.20  
  Purchase #6 $138.71   9.451%   $151.8195   $151.82   $151.80   $151.80  
  Purchase #7 $183.88   7.702%   $198.0424   $198.04   $198.05   $198.00  
  7 purchase totals = $797.11       $874.2013   $874.20   $874.25   $874.20