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 $17.55   7.653%   $18.8931   $18.89   $18.90   $18.90  
  Purchase #2 $202.43   7.731%   $218.0799   $218.08   $218.10   $218.10  
  Purchase #3 $33.99   11.540%   $37.9124   $37.91   $37.90   $37.90  
  Purchase #4 $212.96   12.332%   $239.2222   $239.22   $239.20   $239.20  
  Purchase #5 $67.50   5.445%   $71.1754   $71.18   $71.20   $71.20  
  Purchase #6 $42.83   3.757%   $44.4391   $44.44   $44.45   $44.40  
  Purchase #7 $97.64   9.864%   $107.2712   $107.27   $107.25   $107.30  
  7 purchase totals = $674.90       $736.9933   $736.99   $737.00   $737.00