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 $11.86   3.574%   $12.2839   $12.28   $12.30   $12.30  
  Purchase #2 $199.31   13.870%   $226.9543   $226.95   $226.95   $227.00  
  Purchase #3 $169.64   12.286%   $190.482   $190.48   $190.50   $190.50  
  Purchase #4 $59.54   7.458%   $63.9805   $63.98   $64.00   $64.00  
  Purchase #5 $229.53   8.331%   $248.6521   $248.65   $248.65   $248.70  
  Purchase #6 $53.56   6.491%   $57.0366   $57.04   $57.05   $57.00  
  Purchase #7 $229.58   8.449%   $248.9772   $248.98   $249.00   $249.00  
  7 purchase totals = $953.02       $1,048.3666   $1,048.36   $1,048.45   $1,048.50