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 $73.32   10.851%   $81.276   $81.28   $81.30   $81.30  
  Purchase #2 $177.60   9.313%   $194.1399   $194.14   $194.15   $194.10  
  Purchase #3 $235.77   10.328%   $260.1203   $260.12   $260.10   $260.10  
  Purchase #4 $104.27   11.468%   $116.2277   $116.23   $116.25   $116.20  
  Purchase #5 $28.57   12.273%   $32.0764   $32.08   $32.10   $32.10  
  Purchase #6 $236.99   13.531%   $269.0571   $269.06   $269.05   $269.10  
  Purchase #7 $68.34   5.314%   $71.9716   $71.97   $71.95   $72.00  
  7 purchase totals = $924.86       $1,024.8690   $1,024.88   $1,024.90   $1,024.90