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 $67.27   3.612%   $69.6998   $69.70   $69.70   $69.70  
  Purchase #2 $239.95   5.551%   $253.2696   $253.27   $253.25   $253.30  
  Purchase #3 $26.53   7.653%   $28.5603   $28.56   $28.55   $28.60  
  Purchase #4 $223.46   12.522%   $251.4417   $251.44   $251.45   $251.40  
  Purchase #5 $153.46   10.855%   $170.1181   $170.12   $170.10   $170.10  
  Purchase #6 $40.47   10.729%   $44.812   $44.81   $44.80   $44.80  
  Purchase #7 $171.32   12.340%   $192.4609   $192.46   $192.45   $192.50  
  7 purchase totals = $922.46       $1,010.3624   $1,010.36   $1,010.30   $1,010.40