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 $96.67   7.654%   $104.0691   $104.07   $104.05   $104.10  
  Purchase #2 $54.40   4.178%   $56.6728   $56.67   $56.65   $56.70  
  Purchase #3 $68.60   13.247%   $77.6874   $77.69   $77.70   $77.70  
  Purchase #4 $120.87   13.220%   $136.849   $136.85   $136.85   $136.80  
  Purchase #5 $242.98   12.532%   $273.4303   $273.43   $273.45   $273.40  
  Purchase #6 $237.32   5.220%   $249.7081   $249.71   $249.70   $249.70  
  Purchase #7 $227.30   4.130%   $236.6875   $236.69   $236.70   $236.70  
  7 purchase totals = $1,048.14       $1,135.1042   $1,135.11   $1,135.10   $1,135.10