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 $155.53   13.843%   $177.06   $177.06   $177.05   $177.10  
  Purchase #2 $240.26   12.157%   $269.4684   $269.47   $269.45   $269.50  
  Purchase #3 $154.41   13.371%   $175.0562   $175.06   $175.05   $175.10  
  Purchase #4 $78.29   4.145%   $81.5351   $81.54   $81.55   $81.50  
  Purchase #5 $181.69   11.872%   $203.2602   $203.26   $203.25   $203.30  
  Purchase #6 $41.82   3.651%   $43.3468   $43.35   $43.35   $43.30  
  Purchase #7 $84.68   11.550%   $94.4605   $94.46   $94.45   $94.50  
  7 purchase totals = $936.68       $1,044.1872   $1,044.20   $1,044.15   $1,044.30