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 $192.71   7.247%   $206.6757   $206.68   $206.70   $206.70  
  Purchase #2 $22.57   11.370%   $25.1362   $25.14   $25.15   $25.10  
  Purchase #3 $84.91   8.848%   $92.4228   $92.42   $92.40   $92.40  
  Purchase #4 $72.32   12.221%   $81.1582   $81.16   $81.15   $81.20  
  Purchase #5 $233.79   4.359%   $243.9809   $243.98   $244.00   $244.00  
  Purchase #6 $127.83   11.290%   $142.262   $142.26   $142.25   $142.30  
  Purchase #7 $144.71   9.745%   $158.812   $158.81   $158.80   $158.80  
  7 purchase totals = $878.84       $950.4478   $950.45   $950.45   $950.50