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 $236.97   4.788%   $248.3161   $248.32   $248.30   $248.30  
  Purchase #2 $183.48   12.113%   $205.7049   $205.70   $205.70   $205.70  
  Purchase #3 $92.92   13.839%   $105.7792   $105.78   $105.80   $105.80  
  Purchase #4 $27.25   7.192%   $29.2098   $29.21   $29.20   $29.20  
  Purchase #5 $220.63   12.349%   $247.8756   $247.88   $247.90   $247.90  
  Purchase #6 $132.56   3.819%   $137.6225   $137.62   $137.60   $137.60  
  Purchase #7 $182.60   10.779%   $202.2825   $202.28   $202.30   $202.30  
  7 purchase totals = $1,076.41       $1,176.7906   $1,176.79   $1,176.80   $1,176.80