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 $21.28   3.640%   $22.0546   $22.05   $22.05   $22.10  
  Purchase #2 $64.32   9.818%   $70.6349   $70.63   $70.65   $70.60  
  Purchase #3 $31.66   4.399%   $33.0527   $33.05   $33.05   $33.10  
  Purchase #4 $165.47   10.716%   $183.2018   $183.20   $183.20   $183.20  
  Purchase #5 $182.67   13.372%   $207.0966   $207.10   $207.10   $207.10  
  Purchase #6 $143.57   10.793%   $159.0655   $159.07   $159.05   $159.10  
  Purchase #7 $213.91   9.557%   $234.3534   $234.35   $234.35   $234.40  
  7 purchase totals = $822.88       $909.4595   $909.45   $909.45   $909.60