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 $218.77   4.860%   $229.4022   $229.40   $229.40   $229.40  
  Purchase #2 $143.94   10.285%   $158.7442   $158.74   $158.75   $158.70  
  Purchase #3 $14.33   12.570%   $16.1313   $16.13   $16.15   $16.10  
  Purchase #4 $216.80   4.350%   $226.2308   $226.23   $226.25   $226.20  
  Purchase #5 $33.46   4.811%   $35.0698   $35.07   $35.05   $35.10  
  Purchase #6 $162.43   7.465%   $174.5554   $174.56   $174.55   $174.60  
  Purchase #7 $177.25   3.687%   $183.7852   $183.79   $183.80   $183.80  
  7 purchase totals = $966.98       $1,023.9189   $1,023.92   $1,023.95   $1,023.90