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 $25.64   7.519%   $27.5679   $27.57   $27.55   $27.60  
  Purchase #2 $72.56   11.814%   $81.1322   $81.13   $81.15   $81.10  
  Purchase #3 $238.41   5.734%   $252.0804   $252.08   $252.10   $252.10  
  Purchase #4 $100.80   5.762%   $106.6081   $106.61   $106.60   $106.60  
  Purchase #5 $101.29   10.163%   $111.5841   $111.58   $111.60   $111.60  
  Purchase #6 $15.25   9.332%   $16.6731   $16.67   $16.65   $16.70  
  Purchase #7 $244.76   13.749%   $278.4121   $278.41   $278.40   $278.40  
  7 purchase totals = $798.71       $874.0579   $874.05   $874.05   $874.10