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 $246.45   5.769%   $260.6677   $260.67   $260.65   $260.70  
  Purchase #2 $213.53   5.542%   $225.3638   $225.36   $225.35   $225.40  
  Purchase #3 $149.32   6.700%   $159.3244   $159.32   $159.30   $159.30  
  Purchase #4 $65.35   10.626%   $72.2941   $72.29   $72.30   $72.30  
  Purchase #5 $28.53   6.384%   $30.3514   $30.35   $30.35   $30.40  
  Purchase #6 $135.49   4.713%   $141.8756   $141.88   $141.90   $141.90  
  Purchase #7 $236.58   6.162%   $251.1581   $251.16   $251.15   $251.20  
  7 purchase totals = $1,075.25       $1,141.0351   $1,141.03   $1,141.00   $1,141.20