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 $111.48   11.470%   $124.2668   $124.27   $124.25   $124.30  
  Purchase #2 $151.36   8.786%   $164.6585   $164.66   $164.65   $164.70  
  Purchase #3 $165.89   8.306%   $179.6688   $179.67   $179.65   $179.70  
  Purchase #4 $220.39   6.316%   $234.3098   $234.31   $234.30   $234.30  
  Purchase #5 $32.56   7.439%   $34.9821   $34.98   $35.00   $35.00  
  Purchase #6 $124.26   13.332%   $140.8263   $140.83   $140.85   $140.80  
  Purchase #7 $212.40   9.627%   $232.8477   $232.85   $232.85   $232.80  
  7 purchase totals = $1,018.34       $1,111.5600   $1,111.57   $1,111.55   $1,111.60