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 $43.37   10.113%   $47.756   $47.76   $47.75   $47.80  
  Purchase #2 $210.28   12.257%   $236.054   $236.05   $236.05   $236.10  
  Purchase #3 $227.49   10.232%   $250.7668   $250.77   $250.75   $250.80  
  Purchase #4 $51.78   11.786%   $57.8828   $57.88   $57.90   $57.90  
  Purchase #5 $246.44   10.741%   $272.9101   $272.91   $272.90   $272.90  
  Purchase #6 $64.99   7.465%   $69.8415   $69.84   $69.85   $69.80  
  Purchase #7 $16.55   9.173%   $18.0681   $18.07   $18.05   $18.10  
  7 purchase totals = $860.90       $953.2793   $953.28   $953.25   $953.40