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 $60.54   8.334%   $65.5854   $65.59   $65.60   $65.60  
  Purchase #2 $155.80   11.400%   $173.5612   $173.56   $173.55   $173.60  
  Purchase #3 $200.79   5.188%   $211.207   $211.21   $211.20   $211.20  
  Purchase #4 $112.50   6.597%   $119.9216   $119.92   $119.90   $119.90  
  Purchase #5 $100.71   10.810%   $111.5968   $111.60   $111.60   $111.60  
  Purchase #6 $8.58   10.837%   $9.5098   $9.51   $9.50   $9.50  
  Purchase #7 $152.40   7.167%   $163.3225   $163.32   $163.30   $163.30  
  7 purchase totals = $791.32       $854.7043   $854.71   $854.65   $854.70