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 $138.61   9.503%   $151.7821   $151.78   $151.80   $151.80  
  Purchase #2 $208.99   11.275%   $232.5536   $232.55   $232.55   $232.60  
  Purchase #3 $114.41   4.262%   $119.2862   $119.29   $119.30   $119.30  
  Purchase #4 $120.93   7.575%   $130.0904   $130.09   $130.10   $130.10  
  Purchase #5 $147.80   13.393%   $167.5949   $167.59   $167.60   $167.60  
  Purchase #6 $12.77   3.535%   $13.2214   $13.22   $13.20   $13.20  
  Purchase #7 $56.92   12.467%   $64.0162   $64.02   $64.00   $64.00  
  7 purchase totals = $800.43       $878.5448   $878.54   $878.55   $878.60