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 $56.40   13.325%   $63.9153   $63.92   $63.90   $63.90  
  Purchase #2 $227.67   8.471%   $246.9559   $246.96   $246.95   $247.00  
  Purchase #3 $177.97   4.106%   $185.2774   $185.28   $185.30   $185.30  
  Purchase #4 $250.91   6.569%   $267.3923   $267.39   $267.40   $267.40  
  Purchase #5 $97.66   8.445%   $105.9074   $105.91   $105.90   $105.90  
  Purchase #6 $197.98   6.278%   $210.4092   $210.41   $210.40   $210.40  
  Purchase #7 $191.62   4.666%   $200.561   $200.56   $200.55   $200.60  
  7 purchase totals = $1,200.21       $1,280.4185   $1,280.43   $1,280.40   $1,280.50