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 $93.69   11.745%   $104.6939   $104.69   $104.70   $104.70  
  Purchase #2 $219.96   9.386%   $240.6054   $240.61   $240.60   $240.60  
  Purchase #3 $12.57   9.749%   $13.7954   $13.80   $13.80   $13.80  
  Purchase #4 $83.50   4.731%   $87.4504   $87.45   $87.45   $87.50  
  Purchase #5 $199.88   9.619%   $219.1065   $219.11   $219.10   $219.10  
  Purchase #6 $138.27   10.850%   $153.2723   $153.27   $153.25   $153.30  
  Purchase #7 $163.72   5.772%   $173.1699   $173.17   $173.15   $173.20  
  7 purchase totals = $911.59       $992.0938   $992.10   $992.05   $992.20