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 $244.55   10.151%   $269.3743   $269.37   $269.35   $269.40  
  Purchase #2 $234.30   10.664%   $259.2858   $259.29   $259.30   $259.30  
  Purchase #3 $97.36   6.808%   $103.9883   $103.99   $104.00   $104.00  
  Purchase #4 $66.70   10.602%   $73.7715   $73.77   $73.75   $73.80  
  Purchase #5 $171.31   11.313%   $190.6903   $190.69   $190.70   $190.70  
  Purchase #6 $58.77   9.424%   $64.3085   $64.31   $64.30   $64.30  
  Purchase #7 $75.50   6.390%   $80.3245   $80.32   $80.30   $80.30  
  7 purchase totals = $948.49       $1,041.7432   $1,041.74   $1,041.70   $1,041.80