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 $229.45   3.160%   $236.7006   $236.70   $236.70   $236.70  
  Purchase #2 $86.88   11.599%   $96.9572   $96.96   $96.95   $97.00  
  Purchase #3 $38.53   13.235%   $43.6294   $43.63   $43.65   $43.60  
  Purchase #4 $164.84   3.479%   $170.5748   $170.57   $170.55   $170.60  
  Purchase #5 $125.81   6.781%   $134.3412   $134.34   $134.35   $134.30  
  Purchase #6 $88.75   9.757%   $97.4093   $97.41   $97.40   $97.40  
  Purchase #7 $216.30   5.244%   $227.6428   $227.64   $227.65   $227.60  
  7 purchase totals = $950.56       $1,007.2553   $1,007.25   $1,007.25   $1,007.20