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 $243.28   13.699%   $276.6069   $276.61   $276.60   $276.60  
  Purchase #2 $243.39   6.126%   $258.3001   $258.30   $258.30   $258.30  
  Purchase #3 $154.75   12.366%   $173.8864   $173.89   $173.90   $173.90  
  Purchase #4 $65.75   12.366%   $73.8806   $73.88   $73.90   $73.90  
  Purchase #5 $7.97   4.352%   $8.3169   $8.32   $8.30   $8.30  
  Purchase #6 $148.28   11.713%   $165.648   $165.65   $165.65   $165.60  
  Purchase #7 $98.35   3.335%   $101.63   $101.63   $101.65   $101.60  
  7 purchase totals = $961.77       $1,058.2689   $1,058.28   $1,058.30   $1,058.20